OFFSET
1,1
MATHEMATICA
r[n_] := Reduce[n == x^2 + y^2 + 7z^2, {x, y, z}, Integers]; Reap[For[n = 0, n <= 600, n++, If[r[n] == False, Print[n]; Sow[n]]]][[2, 1]] (* Jean-François Alcover, Feb 08 2016 *)
Take[Module[{c=With[{nn=30}, Union[Flatten[Table[x^2+y^2+7z^2, {x, 0, nn}, {y, 0, nn}, {z, 0, nn}]]]]}, Complement[Range[Max[c]], c]], 60] (* Harvey P. Dale, Dec 16 2018 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Ralf Stephan, Aug 20 2004
STATUS
approved