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A258453 G.f.: Sum_{k>0} x^((k^2 + k)/2) / (1 + x^k). 1
1, -1, 2, -1, 0, 0, 2, -1, -1, 0, 2, 0, 0, -2, 2, -1, 0, 1, 2, -2, 0, -2, 2, 0, 1, 0, 0, 0, 0, -2, 2, -1, 0, 0, 2, 1, 0, -2, 0, -2, 0, 2, 2, -2, 2, -2, 2, 0, -1, -1, 0, 0, 0, -2, 4, 0, 0, 0, 2, -2, 0, -2, 0, -1, 0, 2, 2, 0, 0, -2, 2, -1, 0, 0, 2, -2, -2, 0, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Seiichi Manyama, Table of n, a(n) for n = 1..5000

EXAMPLE

G.f. = x - x^2 + 2*x^3 - x^4 + 2*x^7 - x^8 - x^9 + 2*x^11 - 2*x^14 + 2*x^15 + ...

MATHEMATICA

a[ n_] := If[ n < 0, 0, SeriesCoefficient[ Sum[ x^((k^2 + k)/2) / (1 + x^k), {k, Sqrt[8 n + 1]}], {x, 0, n}]];

PROG

(PARI) {a(n) = if( n<0, 0, polcoeff( sum(k=1, sqrtint(8*n + 1), x^((k^2 + k)/2) / (1 + x^k), x * O(x^n)), n))};

CROSSREFS

Cf. A001227, A048272.

Sequence in context: A291955 A291904 A249808 * A025874 A256012 A263251

Adjacent sequences:  A258450 A258451 A258452 * A258454 A258455 A258456

KEYWORD

sign

AUTHOR

Michael Somos, Nov 05 2015

STATUS

approved

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Last modified August 21 18:38 EDT 2019. Contains 326168 sequences. (Running on oeis4.)