Numbers: The anaesthetist

Today is the 17th of August.

Seventeen, according to Plutarch, was a number to strike fear into the hearts of the Pythagoreans, "For 17 lies midway between 16 and 18, these two being the only numbers representing rectangular areas for which the perimeter equals the area."

Seventeen is the third Fermat prime, being equal to 222 + 1. Fermat conjectured that all numbers of the form 22n + 1 were prime, but Euler disproved it when he discovered that 226 + 1 is divisible by 641. That remains the sole known use for the number 641, which is one more than the number of oil well fires started in Kuwait at the end of the Gulf War.

Seventeen is also:

The tons of gold made into wedding rings each year in the United States;

The average number of times we laugh each day;

The inches allowed for the average human bottom in BR train designs;

The goldfish bowls left on public transport in Tokyo in 1979;

The syllables in a Haiku.

Competition: Spell a number (for example forty-two) then add its letters' place values: (6+15+18+20+25+20+23+15 = 142). Can you find a number that gives itself as the result? Numbers over 100 to be spelt as "One hundred and... etc).

Entries by 29 Aug to: Pastimes, the Independent, 1 Canada Square, Canary Wharf, London E14 5DL. Three Chambers Dictionary prizes for correct answers.

3 August answers: Manchester (mash centre) Sheffield (fed elfish) Nottingham ( man tonight). Winners: PS Lomax, CJ Lee, Mrs A Reed.