A161577 a(1)=2. a(n) = the smallest integer > a(n-1) such that d(a(n)) >= d(n), where d(n) = the number of divisors of n.

2, 3, 4, 6, 7, 8, 9, 10, 12, 14, 15, 18, 19, 20, 21, 24, 25, 28, 29, 30, 32, 33, 34, 36, 38, 39, 40, 42, 43, 48, 49, 50, 51, 52, 54, 60, 61, 62, 63, 66, 67, 70, 71, 72, 75, 76, 77, 80, 81, 84, 85, 88, 89, 90, 91, 96, 98, 99, 100, 108, 109, 110, 112, 114, 115, 120, 121, 124, 125

Offset

1,1

Comments

Starting the sequence with a(1)=1 instead would have lead to a(n) = n for all n, obviously.

Links

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

Mathematica

nxt[{n_, a_}]:=Module[{k=a+1, d=DivisorSigma[0, n+1]}, While[DivisorSigma[0, k]<d, k++]; {n+1, k}]; NestList[nxt, {1, 2}, 80][[All, 2]] (* Harvey P. Dale, Aug 30 2017 *)

Crossrefs

A137518, A161576, A161578

Sequence in context: A296858 A296241 A070932 * A358330 A093686 A325031

Adjacent sequences: A161574 A161575 A161576 * A161578 A161579 A161580

Keyword

nonn

Author

Leroy Quet, Jun 14 2009

Extensions

Extended beyond 20 by R. J. Mathar, Oct 24 2009

Status

approved