A113619 Heptagon-free numbers: numbers k such that no divisor of k is a heptagonal number > 1.

1, 2, 3, 4, 5, 6, 8, 9, 10, 11, 12, 13, 15, 16, 17, 19, 20, 22, 23, 24, 25, 26, 27, 29, 30, 31, 32, 33, 37, 38, 39, 40, 41, 43, 44, 45, 46, 47, 48, 50, 51, 52, 53, 57, 58, 59, 60, 61, 62, 64, 65, 66, 67, 69, 71, 73, 74, 75, 76, 78, 79, 80, 82, 83, 85, 86, 87, 88, 89, 92, 93, 94, 95, 96, 97, 99, 100

Offset

1,2

Comments

Heptagonal number analogy of A112886 (the triangle-free positive integers).

Links

Table of n, a(n) for n=1..77.

Eric Weisstein's World of Mathematics, Heptagonal Number.

Example

7 is the first nontrivial heptagonal number, so no multiple of 7 is a term.

Mathematica

upto=100; Module[{maxhep=Floor[(3+Sqrt[9+40upto])/10], heps}, heps= Rest[ Table[(n(5n-3))/2, {n, maxhep}]]; Complement[Range[upto], Union[ Flatten[ Table[n*heps, {n, Ceiling[upto/7]}]]]]] (* Harvey P. Dale, May 19 2012 *)

Crossrefs

Cf. A000566, A112886, A113502.

Sequence in context: A267305 A302478 A356939 * A376047 A325114 A004765

Adjacent sequences: A113616 A113617 A113618 * A113620 A113621 A113622

Keyword

easy,nonn

Author

Jonathan Vos Post, Jan 14 2006

Extensions

Corrected by Harvey P. Dale, May 19 2012

Status

approved