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A270238
Indices of Pell numbers of the form x^2 + xy + y^2.
0
1, 4, 7, 23, 41, 79, 89, 97, 127, 167, 191, 223, 239, 241, 257, 281, 439, 577, 593
OFFSET
1,2
COMMENTS
Terms of this sequence are prime numbers most of the time.
EXAMPLE
4 is a term because A000129(4) = 12 and 12 = 2^2 + 2*2 + 2^2.
PROG
(PARI) a000129(n) = ([2, 1; 1, 0]^n)[2, 1];
isA003136(n) = #bnfisintnorm(bnfinit(z^2+z+1), n);
for(n=1, 1e3, if(isA003136(a000129(n)), print1(n, ", ")));
CROSSREFS
Sequence in context: A363650 A086968 A101824 * A027946 A348478 A363543
KEYWORD
nonn,more
AUTHOR
Altug Alkan, Mar 18 2016
EXTENSIONS
a(17)-a(19) from Jinyuan Wang, Aug 14 2022
STATUS
approved