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A028601
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Expansion of (theta_3(z)*theta_3(9z) + theta_2(z)*theta_2(9z)).
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2
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1, 0, 2, 0, 0, 4, 0, 0, 2, 4, 0, 0, 0, 0, 0, 0, 0, 4, 4, 0, 4, 0, 0, 0, 0, 0, 4, 0, 0, 4, 0, 0, 2, 0, 0, 0, 4, 0, 0, 0, 0, 4, 0, 0, 0, 8, 0, 0, 0, 0, 6, 0, 0, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 0, 0, 4, 0, 0, 0, 4, 0, 4, 0, 0, 0, 0, 0, 4, 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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MATHEMATICA
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r[n_]:=Reduce[{x, y}.{{2, 1}, {1, 5}}.{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 22 2020 *)
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PROG
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(PARI) a(n) = if(n<1, n==0, qfrep([2, 1; 1, 5], n)[n]*2); \\ Jinyuan Wang, Feb 21 2020
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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