OFFSET
1,2
COMMENTS
a(11) = 391 is first composite number in this sequence.
LINKS
Index entries for linear recurrences with constant coefficients, signature (1,2,-2,-1,1).
FORMULA
a(n) = (A113804(n)^2 - 2)/14. - Amiram Eldar, Aug 13 2024
a(n) = 2*A212965(n-1) - 1. - Hugo Pfoertner, Aug 13 2024
E.g.f.: ((2 + x + 7*x^2)*cosh(x) + (1 - x + 7*x^2)*sinh(x) - 2)/2. - Stefano Spezia, Aug 13 2024
MATHEMATICA
((Table[14*n + {4, 10}, {n, 0, 23}] // Flatten)^2 - 2)/14 (* Amiram Eldar, Aug 13 2024 *)
PROG
(Magma) [k: k in [0..8000] | IsSquare(14*k + 2)];
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Juri-Stepan Gerasimov, Aug 12 2024
STATUS
approved