A053229 Numbers n for which second differences of sigma(n) are negative.

1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 87, 89, 91, 93, 95, 97, 99, 101, 103, 104, 105, 107, 109, 111, 113, 115, 117, 119, 121, 123, 125, 127, 129

Offset

1,2

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..133);

Mathematica

Select[Range[150], DivisorSigma[1, # + 2] - DivisorSigma[1, # + 1] < (DivisorSigma[1, # + 1] - DivisorSigma[1, #]) &] (* G. C. Greubel, Sep 03 2018 *)

Crossrefs

Cf. A000203, A053223, A053228.

Sequence in context: A064679 A081874 A165747 * A157142 A247328 A317107

Adjacent sequences: A053226 A053227 A053228 * A053230 A053231 A053232

Keyword

nonn

Author

Asher Auel, Dec 10 2000

Status

approved