A369386 a(n) is the constant term in expansion of Product_{k=1..n} (x^(2*k-1) + 1/x^(2*k-1))^2.

1, 2, 4, 8, 18, 48, 138, 428, 1392, 4652, 15884, 55124, 193724, 688008, 2465134, 8899700, 32342236, 118215780, 434314138, 1602935104, 5940303754, 22095769648, 82464791420, 308715131744, 1158949678600, 4362040367048, 16456820491806, 62223707844096

Offset: 0

Author

Ilya Gutkovskiy, Jan 22 2024

Keywords

• nonn

Crossrefs

Cf. A047653, A156181, A156700, A292476.

Programs

Mathematica

Table[Coefficient[Product[(x^(2 k - 1) + 1/x^(2 k - 1))^2, {k, 1, n}], x, 0], {n, 0, 27}]