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

1,2

Links

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

Formula

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

Example

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

Mathematica

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

Prog

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

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).

Sequence in context: A160205 A187817 A276678 * A053794 A249913 A003077

Adjacent sequences: A276677 A276678 A276679 * A276681 A276682 A276683

Keyword

nonn

Author

Colin Barker, Sep 13 2016

Status

approved