A113468 Least number k such that k, k+n, k+2*n and k+3*n have the same number of divisors.

242, 213, 3445, 111, 8718, 5, 2001, 69, 3526, 299, 1074, 5, 2222, 537, 9177, 129, 4114, 5, 8, 598, 7843, 111, 1235, 10, 2984, 303, 3538, 417, 987, 7, 1771, 91, 7659, 57, 9269, 10, 2264, 145, 1197, 219, 1606, 5, 1826, 115, 8897, 203, 618, 5, 8, 159, 2673, 183

Offset

1,1

Comments

Fourth row of A113465.

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Example

a(19) = 8 because 8, 8 + 19 = 27, 8 + 2*19 = 46 and 8 + 3*19 = 65 each have 4 divisors.

Mathematica

a[n_] := Module[{k = 1, d}, While[(d = DivisorSigma[0, k]) != DivisorSigma[0, k+n] || DivisorSigma[0, k+2*n] != d || DivisorSigma[0, k+3*n] != d, k++]; k]; Array[a, 60] (* Amiram Eldar, Aug 04 2024 *)

Prog

(PARI) a(n) = {my(k = 1, d); while((d = numdiv(k)) != numdiv(k+n) || numdiv(k+2*n) != d || numdiv(k+3*n) != d, k++); k; } \\ Amiram Eldar, Aug 04 2024

Crossrefs

Cf. A113465.

Sequence in context: A171242 A259092 A060110 * A220089 A039665 A259719

Adjacent sequences: A113465 A113466 A113467 * A113469 A113470 A113471

Keyword

nonn

Author

David Wasserman, Jan 08 2006

Extensions

Name corrected by Amiram Eldar, Aug 04 2024

Status

approved