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A109976
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Diagonal sums of number triangle A109974.
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2
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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
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OFFSET
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0,2
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LINKS
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FORMULA
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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
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MAPLE
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f:= n -> add(numtheory:-sigma[k](n-2*k+1), k=0..n/2):
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MATHEMATICA
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Array[Sum[DivisorSigma[k, (# - 2 k + 1)], {k, 0, Floor[#/2]}] &, 32, 0] (* Michael De Vlieger, May 27 2018 *)
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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