On 04/08/2025 11:16, Ralph Corderoy wrote:
Hi Victor,‘What number is the odd one out, and why: 2 4 6 8 13 19.’2 is the only even prime. 4 is the only square in the list. 6 is the only perfect number in the list. 8 is the only cube in the list. Can't think of an argument for 13 or 19 just now.13 is a happy number, but then so is 19. :-) 1² + 3² = 1 + 9 = 10 1² + 0² = 1 + 0 = 1 https://en.wikipedia.org/wiki/Happy_number OEIS does find anything. https://oeis.org/search?q=2%2C4%2C6%2C8%2C13%2C19&language=english&go=Search I did come up with a second answer the other night: four is the only one with the same number of letters in its spelling as its value. 3 two → 4 four 3 six 5 eight 8 thirteen 8 nineteen But that's not very mathsy, and why give such an awkward sequence when a simpler one would do? 3 one 3 two 5 three → 4 four 4 five 3 six 5 seven
Eight, because it is the only one that starts with a vowel. Also not very mathsy, but it was a pub quiz so may have nothing to do with maths. -- Paul Tansom | Aptanet Ltd. | https://www.aptanet.com/ | 023 9238 0001 ============================================================================= Registered in England | Company No: 4905028 | Registered Office: Ralls House, Parklands Business Park, Forrest Road, Denmead, Waterlooville, Hants, PO7 6XP -- Next meeting: Online, Jitsi, Tuesday, 2025-08-05 20:00 Check to whom you are replying Meetings, mailing list, IRC, ... https://dorset.lug.org.uk New thread, don't hijack: mailto:[email protected]
