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 A205808 G.f.: Sum_{n=-oo..oo} q^(9*n^2 + 2*n). 3
 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0 LINKS G. C. Greubel, Table of n, a(n) for n = 0..1000 S. Cooper and M. D. Hirschhorn, Results of Hurwitz type for three squares. Discrete Math. 274 (2004), no. 1-3, 9-24. See A(q). FORMULA Expansion of f(x^7, x^11) in powers of x where f(, ) is Ramanujan's general theta function. - Michael Somos, Jan 19 2017 Euler transform of a period 36 sequence. - Michael Somos, Jan 19 2017 EXAMPLE G.f. = 1 + x^7 + x^11 + x^32 + x^40 + x^75 + x^87 + x^136 + x^152 + x^215 + ... G.f. = q + q^64 + q^100 + q^289 + q^361 + q^676 + q^784 + q^1225 + q^1369 + ... MATHEMATICA a[ n_] := SeriesCoefficient[ QPochhammer[ -x^7, x^18] QPochhammer[ -x^11, x^18] QPochhammer[ x^18], {x, 0, n}]; (* Michael Somos, Jan 19 2017 *) PROG (PARI) {a(n) = issquare(9*n + 1)}; /* Michael Somos, Jan 19 2017 */ CROSSREFS Characteristic function of A132355. Sequence in context: A082784 A105165 A058342 * A238897 A297199 A185117 Adjacent sequences:  A205805 A205806 A205807 * A205809 A205810 A205811 KEYWORD nonn AUTHOR N. J. A. Sloane, Jan 31 2012 STATUS approved

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Last modified September 20 22:20 EDT 2021. Contains 347596 sequences. (Running on oeis4.)