The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A306469 Numbers not of the form x^2+2*y^2+2*y*z+4*z^2 (with x, y, z all >= 0). 2
 7, 10, 14, 15, 21, 30, 35, 39, 42, 63, 70, 79, 84, 91, 94, 119, 126, 130, 133, 140, 168, 175, 182, 189, 210, 217, 231, 238, 259, 266, 280, 287, 315, 329, 336, 343, 359, 364, 378, 382, 385, 391, 399, 413, 427, 434, 462, 476, 483, 490, 511, 525, 532, 546, 560 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS It appears that the only terms not divisible by 7 are 10, 15, 30, 39, 79, 94, 130, 359, 382, 391, 754, and 1546. - 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 while x^2<=N do for y from 0 while x^2 + 2*y^2 <= N do for z from 0 do v:= x^2 + 2*y^2 + 2*y*z + 4*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 Cf. A097634 (without the nonnegative requirement). Sequence in context: A123834 A064629 A215579 * A059752 A080205 A108980 Adjacent sequences: A306466 A306467 A306468 * A306470 A306471 A306472 KEYWORD nonn AUTHOR N. J. A. Sloane, Mar 26 2019 EXTENSIONS Thanks to Robert Israel for pointing out that I neglected to mention x, y, z >= 0. - N. J. A. Sloane, Mar 27 2019 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified April 17 18:43 EDT 2024. Contains 371765 sequences. (Running on oeis4.)