A306296 Numbers not of the form x^2+7*y^2+7*z^2.

2, 3, 5, 6, 10, 12, 13, 17, 19, 20, 21, 22, 24, 26, 27, 31, 33, 34, 38, 40, 41, 42, 45, 46, 47, 48, 52, 54, 55, 58, 59, 61, 62, 66, 68, 69, 73, 75, 76, 80, 82, 83, 85, 87, 89, 90, 93, 94, 96, 97, 98, 101, 102, 103, 104, 108, 110, 111, 115, 117, 118, 122

Offset

1,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..1356

Irving Kaplansky, The first nontrivial genus of positive definite ternary forms, Mathematics of Computation, Vol. 64 (1995): 341-345.

Mathematica

r[k_]:=Reduce[x>=0&&y>=0&&z>=0&&k==x^2 + 7 y^2 + 7 z^2, {x, y, z}, Integers]; Reap[For[k=1, k<=150, k++, If[r[k]===False, Print[k]; Sow[k]]]][[2, 1]] (* Vincenzo Librandi, Mar 27 2019 *)

Crossrefs

Sequence in context: A138587 A099350 A337218 * A351717 A191173 A240026

Adjacent sequences: A306293 A306294 A306295 * A306297 A306298 A306299

Keyword

nonn

Author

N. J. A. Sloane, Mar 26 2019

Status

approved