A276681 Number of divisors of the n-th octagonal number.

1, 4, 4, 8, 4, 12, 4, 10, 9, 16, 4, 16, 4, 20, 8, 12, 6, 24, 8, 16, 8, 16, 4, 40, 6, 16, 8, 16, 8, 40, 8, 14, 8, 24, 8, 24, 4, 24, 16, 20, 6, 32, 4, 32, 24, 20, 4, 24, 12, 24, 8, 32, 4, 56, 8, 20, 12, 16, 12, 32, 4, 20, 24, 32, 8, 48, 4, 16, 16, 48, 4, 30, 8

Offset

1,2

Links

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

Formula

a(n) = A000005(A000567(n)).

Example

a(4) = 8 because the 4th octagonal number is 40, which has 8 divisors: 1,2,4,5,8,10,20,40.

Prog

(PARI)
pg(m, n) = (n^2*(m-2)-n*(m-4))/2 \\ n-th m-gonal number
vector(150, n, numdiv(pg(8, n)))

Crossrefs

Cf. A000005, A000567.

Cf. A063440 (m=3), A048691 (m=4), A276678 (m=5), A276679 (m=6), A276680 (m=7), A276682 (m=9), A276683 (m=10).

Sequence in context: A082075 A243641 A276620 * A255485 A322328 A095727

Adjacent sequences: A276678 A276679 A276680 * A276682 A276683 A276684

Keyword

nonn

Author

Colin Barker, Sep 13 2016

Status

approved