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
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Mar 26 2019
STATUS
approved