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 A028649 Expansion of (theta_3(z)*theta_3(21z) + theta_2(z)*theta_2(21z)). 1
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Jinyuan Wang, Table of n, a(n) for n = 0..1000 MATHEMATICA 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 *) PROG (PARI) a(n) = if(n<1, n==0, qfrep([2, 1; 1, 11], n)[n]*2); \\ Jinyuan Wang, Feb 21 2020 CROSSREFS Cf. A028650, A028651, A028652. Sequence in context: A275962 A132976 A143840 * A305558 A341624 A341620 Adjacent sequences:  A028646 A028647 A028648 * A028650 A028651 A028652 KEYWORD nonn AUTHOR STATUS approved

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Last modified July 7 13:21 EDT 2022. Contains 355148 sequences. (Running on oeis4.)