A053215 Sum of divisors of those numbers n such that n and n+1 have the same sum of divisors.

24, 312, 1440, 2160, 2688, 2640, 4320, 4464, 7644, 22932, 28314, 29040, 34560, 37440, 51840, 56160, 65280, 100800, 115200, 114912, 120960, 120960, 138240, 153216, 194400, 168960, 178560, 186048, 207360, 221184, 244800, 280800, 276480

Offset: 1

Author

Asher Auel, Jan 11 2000

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10135 (from the b-file at A002961; terms 1..4804 from T. D. Noe)

Crossrefs

Cf. A000203, A002961, A053249.

Programs

Mathematica

Transpose[Select[{DivisorSigma[1,First[#]],DivisorSigma[1,Last[#]]}&/@ Partition[Range[280000],2,1],First[#]==Last[#]&]][[1]] (* Harvey P. Dale, May 07 2012 *)
DivisorSigma[1,#]&/@SequencePosition[DivisorSigma[1,Range[280000]],{x_,x_}][[All,1]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Sep 21 2017 *)

Formula

a(n) = sigma(A002961(n))