A128513 a(1)=2, a(n) = 1 + (smallest integer > a(n-1) with the same number of divisors as a(n-1)).

2, 4, 10, 15, 22, 27, 34, 36, 101, 104, 106, 112, 163, 168, 211, 224, 229, 234, 261, 269, 272, 305, 310, 319, 322, 329, 335, 340, 343, 347, 350, 353, 360, 421, 432, 529, 842, 844, 846, 851, 863, 878, 880, 913, 915, 936, 991, 998

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1001

Example

a(6) = 27, which has 4 positive divisors. The next larger
integer with 4 divisors is 33. So a(7) = 1 + 33 = 34.

Mathematica

a = {2}; n = 3; While[n < 1000, If[Length[Divisors[n]] == Length[Divisors[a[[ -1]]]], AppendTo[a, n + 1]; n++; ]; n++ ]; a (* Stefan Steinerberger, Jun 15 2007 *)
nxt[n_]:=Module[{k=n+1, ds=DivisorSigma[0, n]}, While[DivisorSigma[ 0, k] != ds, k++]; k+1]; NestList[nxt, 2, 50] (* Harvey P. Dale, Aug 03 2016 *)

Crossrefs

Sequence in context: A217134 A351927 A333619 * A048200 A058201 A000947

Adjacent sequences: A128510 A128511 A128512 * A128514 A128515 A128516

Keyword

nonn

Author

Leroy Quet, Jun 12 2007

Extensions

More terms from Stefan Steinerberger, Jun 15 2007

Status

approved