This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A276680 #10 Jun 09 2017 10:49:00 %S A276680 1,2,6,4,4,5,10,6,8,4,8,12,4,4,24,16,4,8,8,8,12,4,16,24,6,4,20,8,4,18, %T A276680 12,10,12,4,16,16,8,8,36,12,4,16,8,16,16,4,12,24,9,12,32,8,4,10,32,12, %U A276680 12,8,8,40,4,4,48,12,16,12,8,8,16,8,20,48,4,4 %N A276680 Number of divisors of the n-th heptagonal number. %H A276680 Colin Barker, <a href="/A276680/b276680.txt">Table of n, a(n) for n = 1..1000</a> %F A276680 a(n) = A000005(A000566(n)). %e A276680 a(3) = 6 because the 3rd heptagonal number is 18, which has 6 divisors: 1,2,3,6,9,18. %t A276680 DivisorSigma[0,PolygonalNumber[7,Range[80]]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Jun 09 2017 *) %o A276680 (PARI) %o A276680 pg(m, n) = (n^2*(m-2)-n*(m-4))/2 \\ n-th m-gonal number %o A276680 vector(100, n, numdiv(pg(7,n))) %Y A276680 Cf. A000005, A000566. %Y A276680 Cf. A063440 (m=3), A048691 (m=4), A276678 (m=5), A276679 (m=6), A276681 (m=8), A276682 (m=9), A276683 (m=10). %K A276680 nonn %O A276680 1,2 %A A276680 _Colin Barker_, Sep 13 2016