A276680 Number of divisors of the n-th heptagonal number.

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, 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, 12, 8, 8, 40, 4, 4, 48, 12, 16, 12, 8, 8, 16, 8, 20, 48, 4, 4

Offset: 1

Author

Colin Barker, Sep 13 2016

Keywords

• nonn

Examples

			a(3) = 6 because the 3rd heptagonal number is 18, which has 6 divisors: 1,2,3,6,9,18.
		

Links

• Colin Barker, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000005, A000566.

Cf. A063440 (m=3), A048691 (m=4), A276678 (m=5), A276679 (m=6), A276681 (m=8), A276682 (m=9), A276683 (m=10).

Programs

Mathematica

DivisorSigma[0,PolygonalNumber[7,Range[80]]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jun 09 2017 *)

PARI

pg(m, n) = (n^2*(m-2)-n*(m-4))/2 \\ n-th m-gonal number
vector(100, n, numdiv(pg(7,n)))

Formula

a(n) = A000005(A000566(n)).