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A109976 Diagonal sums of number triangle A109974. 2
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 (list; graph; refs; listen; history; text; internal format)
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: A137604 A034901 A275390 * A011768 A052487 A067951

Adjacent sequences:  A109973 A109974 A109975 * A109977 A109978 A109979

KEYWORD

easy,nonn

AUTHOR

Paul Barry, Jul 06 2005

STATUS

approved

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Last modified October 16 11:23 EDT 2019. Contains 328056 sequences. (Running on oeis4.)