A161576 a(1)=1. a(n) = the smallest integer > a(n-1) such that d(a(n)) > d(n), where d(n) = the number of divisors of n.

1, 4, 6, 8, 9, 12, 14, 16, 18, 20, 21, 24, 25, 28, 30, 32, 33, 36, 38, 40, 42, 44, 45, 48, 50, 52, 54, 56, 57, 60, 62, 64, 66, 68, 70, 72, 74, 75, 76, 80, 81, 84, 85, 88, 90, 92, 93, 96, 98, 100, 102, 104, 105, 108, 110, 112, 114, 116, 117, 120, 121, 124, 126, 128, 130, 132

Offset

1,2

Links

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

Maple

with(numtheory): a := proc (n) local j: if n = 1 then 1 else for j from a(n-1)+1 while tau(j) <= tau(n) do end do: j end if end proc: seq(a(n), n = 1 .. 70); # Emeric Deutsch, Jul 11 2009

Mathematica

si[{n_, a_}]:=Module[{k=a+1, d=DivisorSigma[0, n+1]}, While[DivisorSigma[0, k]<=d, k++]; {n+1, k}]; NestList[si, {1, 1}, 70][[All, 2]] (* Harvey P. Dale, Nov 12 2017 *)

Crossrefs

Cf. A137518, A161577, A161578.

Sequence in context: A231573 A327204 A047409 * A327446 A100425 A258614

Adjacent sequences: A161573 A161574 A161575 * A161577 A161578 A161579

Keyword

nonn

Author

Leroy Quet, Jun 14 2009

Extensions

Extended by Emeric Deutsch, Jul 11 2009

Status

approved