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A216512 Number of nonnegative integer solutions to the equation a^2 + 7*b^2 = n. 2
1, 0, 0, 1, 0, 0, 1, 1, 1, 0, 1, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 1, 1, 0, 0, 2, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 3, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,16

LINKS

Table of n, a(n) for n=1..87.

MATHEMATICA

r[n_] := Reduce[x >= 0 && y >= 0 && x^2 + 7 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, 87}] (* Jean-Fran├žois Alcover, Jun 24 2017 *)

CROSSREFS

Cf. A020670.

Sequence in context: A216577 A096562 A096563 * A078359 A107329 A263717

Adjacent sequences:  A216509 A216510 A216511 * A216513 A216514 A216515

KEYWORD

nonn

AUTHOR

V. Raman, Sep 08 2012

STATUS

approved

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Last modified October 25 05:19 EDT 2021. Contains 348239 sequences. (Running on oeis4.)