A053247 Second differences of sigma(n) that are positive.

2, 7, 11, 7, 22, 24, 7, 34, 41, 14, 48, 40, 18, 68, 71, 21, 49, 75, 38, 102, 92, 100, 103, 47, 110, 96, 50, 138, 140, 15, 103, 134, 78, 195, 161, 6, 116, 194, 70, 182, 140, 72, 234, 178, 56, 156, 227, 76, 229, 218, 226, 276, 160, 260, 162, 26, 252, 280, 74, 224

Offset: 1

Author

Asher Auel, Jan 11 2000

Keywords

• nonn

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000203, A053223, A053248.

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

Select[Differences[DivisorSigma[1,Range[150]],2],#>0&] (* Harvey P. Dale, May 10 2012 *)

Formula

a(n) = A053223(A053228(n))