A053248 Second differences of sigma(n) that are negative.

1, 4, 10, 9, 11, 30, 10, 20, 40, 32, 16, 65, 13, 42, 82, 46, 12, 96, 26, 82, 106, 46, 18, 143, 57, 70, 114, 88, 40, 214, 26, 66, 136, 88, 120, 244, 30, 60, 160, 171, 47, 256, 36, 150, 266, 96, 40, 286, 88, 176, 226, 124, 12, 24, 342, 170, 230, 222, 94, 34, 443, 71

Offset: 1

Author

Asher Auel, Jan 11 2000

Keywords

• nonn

Crossrefs

Cf. A000203, A053223, A053247.

Programs

Maple

with (numtheory): f := [seq( sigma(i+2) - sigma(i+1) - (sigma(i+1) - sigma(i)), i=1..200)];
seq(`if`(f[i] < 0,f[i],print( )), i=1..200);

Mathematica

Abs[Select[Differences[DivisorSigma[1,Range[200]],2],Negative]] (* Harvey P. Dale, Aug 13 2015 *)

Formula

a(n) = A053223(A053229(n)).