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A028649
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Expansion of (theta_3(z)*theta_3(21z) + theta_2(z)*theta_2(21z)).
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1
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1, 0, 2, 0, 0, 0, 0, 0, 2, 0, 0, 4, 0, 0, 0, 4, 0, 0, 2, 0, 0, 0, 0, 4, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 4, 0, 0, 0, 0, 0, 0, 2, 0, 4, 0, 0, 0, 0, 0, 6, 4, 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 4, 2, 0, 4, 0, 0, 0, 0, 0, 0
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OFFSET
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0,3
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LINKS
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Jinyuan Wang, Table of n, a(n) for n = 0..1000
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MATHEMATICA
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r[n_]:=Reduce[{x, y}.{{2, 1}, {1, 11}}.{x, y}==n, {x, y}, Integers]; Table[rn=r[n]; Which[rn===False, 0, Head[rn]===Or, Length[rn], Head[rn]===And, 1], {n, 0, 105}] (* Vincenzo Librandi, Feb 23 2020 *)
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PROG
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(PARI) a(n) = if(n<1, n==0, qfrep([2, 1; 1, 11], n)[n]*2); \\ Jinyuan Wang, Feb 21 2020
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CROSSREFS
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Cf. A028650, A028651, A028652.
Sequence in context: A275962 A132976 A143840 * A305558 A341624 A341620
Adjacent sequences: A028646 A028647 A028648 * A028650 A028651 A028652
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane
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STATUS
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approved
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