Numbers

Today is the 31st of March.

Numerically, 31 is the third Mersenne prime, of the form 2n-1, and is one of only two numbers expressible in two different ways as the sum of successive powers:

31 = 1+5+52 = 1+2+22+23+24

(the other such number is 8191).

Thirty-one is also:

The gestation period, in days, of a rabbit.

The bones in a human leg.

The ideal score in cribbage.

The mean Fahrenheit temperature in Denmark in February.

The days and nights under a cold stone for the toad in the witches' spell in Macbeth.

COMPETITION:

A somewhat T in C edition of our "26 L of the A" (Letters of the Alphabet) format this week. We have three Chambers Dictionaries for decoding the following. Try tomorrow if you can't solve them today:

2 M C S T B

4 H a J G F

9 G F N

A in 1d

A 4 1, 1 4 A (T 3 M).

Entries, by 12 April, to: Pastimes, the Independent, 1 Canada Square, Canary Wharf, London E14 5DL.

17 March Competition report:

13 Unlucky for Some; 15 Minutes Everyone will be famous (Andy Warhol); 21 Points (Pips) on a Die (Dice); 21 Shillings in a Guinea; 25 Years for a Silver Wedding. Prizes to Anne Key (Oxon), John Whiting (St John's Wood), Jean Drane (Ealing).