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 A306989 Numbers not of the form x^2+2*y^2+7*z^2. 1
 5, 14, 20, 21, 35, 42, 70, 84, 91, 119, 133, 140, 158, 168, 182, 189, 217, 231, 238, 245, 266, 280, 287, 315, 329, 336, 364, 378, 385, 413, 427, 434, 462, 476, 483, 511, 518, 525, 532, 560, 574, 581, 609, 623, 630, 658, 672, 679, 686, 707, 721, 728, 756, 770 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS It appears that the only terms not divisible by 7 are 5, 29 and 158. - Robert Israel, Mar 27 2019 LINKS Robert Israel, Table of n, a(n) for n = 1..10000 Irving Kaplansky, The first nontrivial genus of positive definite ternary forms, Mathematics of Computation, Vol. 64 (1995): 341-345. MAPLE N:= 1000: # for terms <= N V:= Array(0..N): for x from 0 to floor(sqrt(N)) do for y from 0 to floor(sqrt((N-x^2)/2)) do for z from 0 do v:= x^2 + 2*y^2 + 7*z^2; if v > N then break fi; V[v]:= 1; od od od: select(t -> V[t]=0, [\$1..N]); # Robert Israel, Mar 27 2019 CROSSREFS Sequence in context: A022139 A277351 A143707 * A003248 A353974 A071317 Adjacent sequences: A306986 A306987 A306988 * A306990 A306991 A306992 KEYWORD nonn AUTHOR N. J. A. Sloane, Mar 26 2019 STATUS approved

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Last modified May 21 19:35 EDT 2024. Contains 372738 sequences. (Running on oeis4.)