Heptagony
I was surfing the internet recently, and found a reference to polygonal numbers. These are series such as the triangular numbers, pentagonal numbers and others, including the series of heptagonal numbers, which starts 1, 7, 18, 34… I asked my nephew to tell me the next member of this series, which he said was 55. Later he told me that he had found a set of six consecutive heptagonal numbers, all less than two million, where the difference between the first and last was divisible by all of the digits 1 to 9. One of the intermediate heptagonal numbers in this set was divisible by just four of these digits.
What was this heptagonal number?
WIN £15 will be awarded to the sender of the first correct answer opened on Wednesday 14 December. The Editor’s decision is final. Please send entries to Enigma 1672, Â鶹´«Ã½, Lacon House, 84 Theobald’s Road, London WC1X 8NS, or to enigma@newscientist.com (please include your postal address).
Answer to 1666 Siblings to infinity: Monday is 257149
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The winner Susan Llewellyn of Huddersfield, West Yorkshire, UK
When this article was first posted, it incorrectly mentioned a set of five consecutive heptagonal numbers.
