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 A216278 Number of solutions to the equation x^2+2y^2 = n with x and y > 0. 2
 0, 0, 1, 0, 0, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 1, 1, 1, 0, 0, 1, 0, 1, 0, 0, 2, 0, 0, 0, 0, 0, 2, 1, 0, 1, 0, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 1, 0, 0, 2, 0, 0, 2, 0, 0, 2, 0, 1, 0, 0, 0, 0, 0, 0, 2, 1, 1, 0, 0, 0, 1, 1, 0, 1, 1, 0, 0, 0, 0, 2, 1, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 0, 3, 0, 0, 2, 0, 0, 0, 0, 1, 2, 0, 0, 0, 0, 1, 2, 0, 0, 0, 1, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,27 LINKS MATHEMATICA r[n_] := Reduce[x > 0 && y > 0 && x^2 + 2 y^2 == n, Integers]; a[n_] := Which[rn = r[n]; rn === False, 0, Head[rn] === And, 1, Head[rn] === Or, Length[rn], True, -1]; Table[a[n], {n, 1, 120}] (* Jean-François Alcover, Jun 24 2017 *) CROSSREFS Cf. A092573, A119395, A000161, A025426. Sequence in context: A257403 A326559 A083339 * A133827 A176192 A028633 Adjacent sequences:  A216275 A216276 A216277 * A216279 A216280 A216281 KEYWORD nonn AUTHOR V. Raman, Sep 03 2012 STATUS approved

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Last modified August 19 18:51 EDT 2019. Contains 326133 sequences. (Running on oeis4.)