login
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
OFFSET
1,16
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-François Alcover, Jun 24 2017 *)
CROSSREFS
Cf. A020670.
Sequence in context: A216577 A096562 A096563 * A078359 A107329 A263717
KEYWORD
nonn
AUTHOR
V. Raman, Sep 08 2012
STATUS
approved