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A097633 Numbers not of form x^2 + y^2 + 7z^2. 2
3, 6, 14, 19, 21, 22, 31, 35, 42, 51, 55, 66, 70, 84, 91, 94, 119, 133, 139, 140, 142, 147, 154, 159, 166, 168, 182, 189, 214, 217, 231, 235, 238, 266, 280, 283, 287, 294, 315, 322, 329, 336, 364, 378, 385, 406, 413, 427, 434, 439, 462, 476, 483, 511, 525 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..55.

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-Fran├žois 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

Complement of A000394.

Sequence in context: A084168 A075390 A118523 * A263620 A083356 A096337

Adjacent sequences:  A097630 A097631 A097632 * A097634 A097635 A097636

KEYWORD

nonn

AUTHOR

Ralf Stephan, Aug 20 2004

STATUS

approved

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Last modified June 14 09:06 EDT 2021. Contains 345018 sequences. (Running on oeis4.)