A053228 n for which second differences of sigma(n) are positive.

2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126, 128, 130, 132

Offset

1,1

Links

G. C. Greubel, Table of n, a(n) for n = 1..10000

Maple

with(numtheory): seq(`if`(sigma(i+2)-sigma(i+1)>(sigma(i+1)-sigma(i)), i, print( )), i=1..142);

Mathematica

Select[Range[150], DivisorSigma[1, #+2] - DivisorSigma[1, #+1] > (DivisorSigma[1, # + 1] - DivisorSigma[1, #]) &] (* G. C. Greubel, Sep 03 2018 *)
Position[Differences[#, 2]&/@Partition[DivisorSigma[1, Range[140]], 3, 1], _?(Positive[ #]&)][[All, 1]] (* Harvey P. Dale, Jan 18 2023 *)

Crossrefs

Cf. A000203, A053223, A053229.

Sequence in context: A105360 A306720 A084564 * A368861 A141098 A084563

Adjacent sequences: A053225 A053226 A053227 * A053229 A053230 A053231

Keyword

nonn

Author

Asher Auel, Jan 10 2000

Status

approved