By way of explanation, and in mathsy celebration of St David's Day, I offer below a handful of mathematical somethings with a Welsh bent, peppered with one or two suggested explorations or diversions that teachers may wish to share and use with students on the day or, indeed, any other.

Dydd Gŵyl Dewi Hapus.

Click to jump to:

- The Equals Sign
- The first use of π to denote C/d
- The Online Encyclopedia of Integer Sequences
- 36
- Bertrand Russell

**The Equals Sign**

(Click here to go back to the menu)

Welsh Doctor and mathematician Robert Recorde, born in 1510 in Tenby, Pembrokeshire, South Wales, was a popular author of a number of mathematical books — which he wrote, unusually for the time, in the English vernacular, thus making his writing more accessible than most scholarly books of the age, which were usually written in Latin.

In his 1557 book,

*The Whetstone of Witte, whiche is the seconde parte of Arithmetike: containyng thextraction of Rootes: The Cossike practise, with the rule of Equation: and the woorkes of Surde Nombers*[1]

*(which you can peruse electronically here),*

*Recorde 'invented' the '=' symbol, 'to avoide the tediouse repetition of these woordes : is equalle to :', which he had already used some 200 times in the book [2].*

Recorde was also, for example, and in the same book, the first to use the plus and minus signs in English: 'There be other 2 signes in often use of which the first is made thus + and betokeneth more: the other is thus made – and betokeneth lesse'. And neither was there an easy way in the 16th century of denoting the powers of numbers, so Recorde coined the now unsurprisingly obsolete term ‘zenzizenzizenzic' [3] to ‘doeth represent the square of squares squaredly’, or in other words to denote the square of the square of a number's square:

\[{\left( {{{\left( {{n^2}} \right)}^2}} \right)^2} = {n^8}\]

Recorde also used another word (which didn't quite catch on), the 'sursolid', meaning to be raised to a prime number greater than three. So a power of five would be the first sursolid, a power of seven the second sursolid, a power of eleven the third, and so on.

Suggested explorations/diversions with/for students:

- Find the zenzizenzizenzic of n for 0 < n < 10.
- Devise questions in
*Recordian*notation and answer them, for example: 'What is the fourth sursolid of two divided by the zenzizenzizenic of two? Give your answer in modern and*Recordian*form'. - Consider and explore the difference between:

\[{\left( {{{\left( {{n^2}} \right)}^2}} \right)^2}\;{\rm{and}}\;{n^{{2^{{2^2}}}}}\]

**The first use of π to denote C/d**

Before being denoted π, the ratio of the circumference of a circle to its diameter was referred to typically in the Latin '

*quantitas in quam cum multiflicetur diameter, proveniet circumferencia*('the quantity which, when the diameter is multiplied by it, yields the circumference)' (Rothman, 2009).

Welsh mathematician William Jones, born in 1675 in Llanfihangel Tre'r Beirdd, on the Isle of Anglesey, North Wales, was the first person to use π to denote the ratio of a circle's circumference to its diameter, doing so in his 1706 book

*Synopsis palmariorum matheseos: or, A new introduction to mathematics: containing the principles of arithmetic & geometry demonstrated, in a short and easie method; with their application to the most useful parts thereof ... Design'd for the benefit, and adapted to the capacities of beginners*[4]. You can peruse the book electronically here [5].

This first ever appearance of π denoting the ratio of a circle's circumference to its diameter can be seen on p243, then more explicitly on p263, as excerpted below. It can also be seen that Jones gave π correct to 100 decimal places, 'as Computed by the Accurate and Ready Pen of the Truly Ingenious Mr.

*John Machin*', using an infinite series whose sum converged to π (see this on 'Machin's Formula' from Peter Rowlett in The Aperiodical).

*Diameter*and the

*Circumference*can never be expres'sd in Numbers' [6]. Jones recognised, as such, that 'to represent an ideal that can be approached but never reached.... only a pure platonic symbol would suffice' (Rothman, 2009).

Jones' use of π as C/d was popularised when the great Swiss mathematician Leonhard Euler adopted it in his

*Introductio in analysin infinitorum*(Introduction to the Analysis of the Infinite) in 1748 [7].

Suggested explorations/diversions with/for students:

- Share the excerpts above with students and try to make sense of them together.
- Have students work out their π-related birthdays, past or future, discussing precision (see this post).
- Note, for example, that at some point on St Davids' Day 2018:
- 3 year-olds born on 8 January 2015, will be π years old.
- 9 year-olds born on 17 April 2008, will be ππ years old.
- 36 year-olds born on 8 January 2015, will be π
^{π}years old.

**The OEIS**

(Click here to go back to the menu)

Mathematician Neil Sloane, born on 10 October 1939 in Beaumaris, North Wales — described by Erica Klarreich as 'The Connoisseur of Number Sequences' in this article in Quanta magazine, and as 'the Guy who Sorts All the World's Numbers in his Attic' in this reprint of the article in Wired — is considered by some to be one of the most influential mathematicians of our time, because in 1964 Sloane founded The Online Encyclopedia of Integer Sequences (OEIS).

The OEIS, as the name suggests — or

*Sloane*, as it is often referred to by its users — is an online database of at the current count, over one quarter of a million integer sequences. It is designed to be used by researchers in mathematics, but as John Conway and Tim Hsu put it in 2006, 'most Nerds should be able to get some enjoyment out of it'.

Enjoy this short selection of some gems that I first discovered through the OEIS:

- Look and Say sequence
- 1, 11, 21, 1211, 111221, 312211, 13112221, 1113213211, ...
- Emirps
- 13, 17, 31, 37, 71, 73, 79, 97, ...
- McNugget Numbers
- 0, 6, 9, 12, 15, 18, 20, 21, 24, 26, 27, 29, ...
- Not McNugget Numbers
- 1, 2, 3, 4, 5, 7, 8, 10, 11, 13, ... 43
- Dihedral calculator primes
- 2, 5, 11, 101, 181, 1181, 1811, 18181, ...
- Home Primes
- 1, 2, 3, 211, 5, 23, 7, 3331113965338635107, 311, 773, 11, ...
- Zig numbers
- 1, 1, 5, 61, 1385, 50521, 2702765, 199360981, ...
- Zag numbers
- 1, 2, 16, 272, 7936, 353792, 22368256, 1903757312, ..

And consider this sequence (sequence A168087): a(n) = the smallest number whose Welsh name (masculine or feminine versions) in the modern Decimal System contains n letters of the alphabet. (For example, 224, dau gant dau ddeg pedwar, is the 20th number in the sequence, and is the smallest number with 20 letters.)

2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|

1 | 2 | 3 | 7 | 4 | 11 | 12 | 15 | 16 | 14 | 27 | 24 | 47 | 44 | 127 | 124 | 147 | 144 | 244 |

Suggested explorations/diversions with/for students:

- Try and ascertain the rule that describes each of my selection of 'gems' above.
- For sequence A168087:
- Continue the sequence to n = 40.
- Find a(100).
- Do the same for sequence A168085 (using the traditional Vigesimal System).
- Generate the same sequence for numbers in English, and other languages.
- Describe this sequence 4, 2, 3, 3, 6, 4, 6, 5, 4, 3, 3, 8, 5... (sequence A140396), entered into the OEIS by Sloane himself in 2008, perhaps as a nod to his Welsh heritage.
- Generate a sequence of numbers that have the same amount of letters in Welsh as in English. For example, a(1) = 2, because 'two' in English and 'dau' in Welsh has 3 letters.
- Maybe submit the sequence to the OEIS (it's not there; I've checked) on behalf of a student (with parental consent of course) who generates it and defines it best, according to the OEIS' format.
- Try this puzzle set by Sloane in Quanta Magazine:
- Can you figure out the 'simple' rule that describes this sequence 13, 26, 2, 4, 6, 3, 9, 12, 8, 10, 5, 15, 18, 14, 7, 21, 24, 16, … (click here for the solution when you're ready).
- The image below shows the 'zigzag triangle', via JohnConway and Tim Hsu (2006). On the LHS of the triangle are the Zig (or secant or Euler) numbers, and on the RHS are the Zag (or tangent) numbers.
- Find the next Zig and Zag numbers.
- How far can you keep going?

**T**

**The Number 36**

(Click here to go back to the menu)

Charles Yang, associate professor in the University of Pennsylvania Department of Linguistics, and not Welsh, has shown (2005, cf. 2015) that if there is a linguistic rule, a generalisation in other words that can be applied to a set of

*N*words, but within this set of

*N*words there is a subset of words,

*e*, that do not follow this rule and that must therefore be memorised, then

\[e < {\theta _N}\;where\;{\theta _N}: = \frac{N}{{\ln \left( N \right)}}\]

This model, dubbed the 'Tolerance Principle', can be applied to how we, as children, learn to count. In short (see this post, 'On 73', for more detail), by using the Tolerance Principle, we can find the least amount of words that we need to learn ‘to overcome the exceptions we have to memorise’. In Welsh, in the modern Decimal System of counting, the numbers 1 to 10 are the only 'exceptions': Un (one), Dau (two), Tri (three), Pedwar (four), Pump (five), Chwech (six), Saith (seven), Wyth (eight), Naw (nine), and Deg (ten). All numbers beyond this are generalised

*from*them, for example eleven is un deg un (one ten one), twelve is un deg dau (one ten two), seventy three is saith deg tri (seven ten three), etc. Thus, the smallest value of

*N*in Welsh such that

*θ*

_{N}= 10 is 36:

\[\begin{array}{l}\begin{align}N &= 36\;\\\because10 &= e < {\theta _N} = \frac{{36}}{{\ln \left( {36} \right)}}\\\;where\;{\rm{ }}\frac{{36}}{{\ln \left( {36} \right)}} &= 10.045991...\end{align}\end{array}\]

Or in other words, once a child has learned to count to 36 in Welsh, they have learned the rules of the game sufficiently to overcome the cognitive need for memorisation, and thus to keep going.

**Bertrand Russell**

Bertrand Russell, the mathematician, logician and humanist, was born on 18 May 1872, in Trellech, Monmouthshire. Russell lived for most of his later years at Plas Penrhyn in Penrhyndeudraeth, Merioneth, North Wales, with a view south to Cardigan Bay and north to the mountains of Eryri (Snowdownia). He died at Plas Penrhyn on February 2, 1970 (read his obituary in the New York Times here), was cremated at Colwyn Bay and had his ashes scattered over the Welsh hills.

Russell won a scholarship to read mathematics at Trinity College, Cambridge University, and with Alfred North Whitehead wrote his monumental three-volume work,

*Principia Mathematica,*between 1910 and 1913. ('Logicomix: An Epic Search for Truth', a wondrous graphic novel 'inspired by the epic story of the quest for the Foundations of Mathematics', described Russell and Whitehead's

*Principia as '*a heroic intellectual adventure.') In 1950, Russell was made a Nobel Laureate in Literature “in recognition of his varied and significant writings in which he champions humanitarian ideals and freedom of thought”.

Read a short biography of Russell here, and watch his 1959 BBC 'Face to Face' interview with John Freeman here, and/or read the transcript here.

**Notes, References & Links:**