A113467 Least k such that k, k+n and k+2n have the same number of divisors.

33, 3, 119, 3, 77, 5, 8, 3, 77, 3, 35, 5, 8, 3, 187, 6, 21, 5, 8, 3, 145, 33, 39, 5, 8, 39, 8, 3, 33, 7, 15, 12, 189, 3, 28, 7, 21, 3, 55, 3, 33, 5, 8, 66, 209, 69, 35, 5, 8, 3, 115, 39, 141, 5, 51, 6, 8, 27, 15, 7, 21, 66, 95, 3, 40, 5, 27, 3, 8, 15, 35, 7, 69, 55, 287, 6, 65, 11, 8, 3, 24

Offset

1,1

Comments

Third row of A113465.

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Example

a(7) = 8 because 8, 15 and 22 each have 4 divisors.

Mathematica

snd[n_]:=Module[{k=1}, While[Length[Union[DivisorSigma[0, {k, k+n, k+2n}]]]>1, k++]; k]; Array[snd, 90] (* Harvey P. Dale, Aug 20 2017 *)

Prog

(PARI) a(n) = {k  = 1; until ((numdiv(k) == numdiv(k+n)) && (numdiv(k) == numdiv(k+2*n)), k++); return (k); } \\ Michel Marcus, Jun 16 2013

Crossrefs

Cf. A005238, A113458, A113465.

Sequence in context: A333128 A135088 A346496 * A113458 A120584 A236177

Adjacent sequences: A113464 A113465 A113466 * A113468 A113469 A113470

Keyword

easy,nonn

Author

David Wasserman, Jan 08 2006

Status

approved