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

1,1

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)

Formula

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

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 *)

Crossrefs

Cf. A000203, A002961, A053249.

Sequence in context: A125436 A096821 A168303 * A290939 A004413 A319554

Adjacent sequences: A053212 A053213 A053214 * A053216 A053217 A053218

Keyword

nonn

Author

Asher Auel, Jan 11 2000

Status

approved