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A359937
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a(n) = Sum_{d|n, d-1 is square} d.
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5
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1, 3, 1, 3, 6, 3, 1, 3, 1, 18, 1, 3, 1, 3, 6, 3, 18, 3, 1, 18, 1, 3, 1, 3, 6, 29, 1, 3, 1, 18, 1, 3, 1, 20, 6, 3, 38, 3, 1, 18, 1, 3, 1, 3, 6, 3, 1, 3, 1, 68, 18, 29, 1, 3, 6, 3, 1, 3, 1, 18, 1, 3, 1, 3, 71, 3, 1, 20, 1, 18, 1, 3, 1, 40, 6, 3, 1, 29, 1, 18, 1, 85, 1, 3
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OFFSET
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1,2
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LINKS
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FORMULA
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G.f.: Sum_{k>=0} (k^2+1) * x^(k^2+1)/(1 - x^(k^2+1)).
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MATHEMATICA
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Table[Sum[If[IntegerQ[Sqrt[d-1]], d, 0], {d, Divisors[n]}], {n, 1, 100}] (* Vaclav Kotesovec, Jan 21 2023 *)
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PROG
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(PARI) a(n) = sumdiv(n, d, issquare(d-1)*d);
(PARI) my(N=100, x='x+O('x^N)); Vec(sum(k=0, sqrtint(N), (k^2+1)*x^(k^2+1)/(1-x^(k^2+1))))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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