OFFSET
1,2
COMMENTS
Discriminant 24.
Multiplied by -1, these are the nonpositive norms of numbers in Z[sqrt(6)]. - Alonso del Arte, Sep 26 2014
Nonnegative integers of the form 2*x^2 - 3*y^2. - Robert Israel, Jun 03 2018
Nonnegative integers of the form 6*x^2 - y^2. - Jon E. Schoenfield, Jun 03 2022
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
N. J. A. Sloane et al., Binary Quadratic Forms and OEIS (Index to related sequences, programs, references)
Math Stackexchange, Can the integers n expressible as 2a^2-3b^2 be classified?
MAPLE
filter:= proc(n) local F;
F:= map(proc(t) local p; p:= t[1] mod 24; if t[2]::even or member(p, {3, 1, 19}) then NULL else p fi end proc, ifactors(n)[2]);
if convert(F, set) intersect {7, 11, 13, 17} <> {} then return false fi;
nops(F)::odd
end proc:
filter(0):= true:
select(filter, [$0..400]); # Robert Israel, Jun 03 2018
MATHEMATICA
Reap[For[n = 0, n <= 300, n++, If[Reduce[-x^2 + 4*x*y + 2*y^2 == n, {x, y}, Integers] =!= False, Sow[n]]]][[2, 1]]
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, May 31 2014
STATUS
approved