A175265 a(1)=1. a(n) = the smallest integer > a(n-1) where |d(a(n)) - d(a(n-1))| = 1; d(n) is the number of divisors of n.

1, 2, 4, 5, 9, 10, 16, 18, 64, 66, 100, 102, 196, 208, 225, 230, 256, 258, 441, 442, 484, 488, 676, 678, 729, 730, 1089, 1090, 1156, 1158, 1225, 1235, 1444, 1446, 1521, 1526, 2116, 2118, 2601, 2607, 3025, 3026, 3249, 3262, 3364, 3367, 3844, 3846, 4225, 4233

Offset

1,2

Links

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

Mathematica

nxt[n_]:=Module[{k=n+1}, While[Abs[DivisorSigma[0, n]-DivisorSigma[0, k]] != 1, k++]; k]; NestList[nxt, 1, 50] (* Harvey P. Dale, Oct 10 2012 *)

Crossrefs

A175266

Sequence in context: A280729 A363283 A213011 * A320225 A070924 A351993

Adjacent sequences: A175262 A175263 A175264 * A175266 A175267 A175268

Keyword

nonn

Author

Leroy Quet, Mar 18 2010

Extensions

More terms from Jon E. Schoenfield, Jun 13 2010

Status

approved