A109976 Diagonal sums of number triangle A109974.

1, 2, 3, 6, 7, 16, 19, 46, 66, 159, 274, 667, 1320, 3263, 7156, 18084, 42794, 111018, 278752, 743889, 1959482, 5383395, 14761634, 41740307, 118517301, 344580865, 1009349749, 3013665637, 9081346743, 27808754039, 86015003997, 269796018547

Offset

0,2

Links

Robert Israel, Table of n, a(n) for n = 0..1063

Formula

a(n) = Sum_{k=0..floor(n/2)} sigma_k(n-2k+1). - Corrected by Robert Israel, May 25 2018

G.f.: Sum_{n>=1} x^(n-1)/((1-x^n)*(1-n*x^2)). - Robert Israel, May 27 2018

Maple

f:= n -> add(numtheory:-sigma[k](n-2*k+1), k=0..n/2):
map(f, [$0..50]); # Robert Israel, May 25 2018

Mathematica

Array[Sum[DivisorSigma[k, (# - 2 k + 1)], {k, 0, Floor[#/2]}] &, 32, 0] (* Michael De Vlieger, May 27 2018 *)

Crossrefs

Cf. A109974

Sequence in context: A034901 A343149 A275390 * A011768 A052487 A067951

Adjacent sequences: A109973 A109974 A109975 * A109977 A109978 A109979

Keyword

easy,nonn

Author

Paul Barry, Jul 06 2005

Status

approved