A068202 Next-to-middle coefficient in expansion of Product_{k=1..n} (1 + x^k).

0, 1, 1, 2, 3, 5, 8, 13, 23, 39, 69, 123, 219, 396, 719, 1313, 2406, 4435, 8215, 15260, 28431, 53167, 99774, 187615, 353500, 667874, 1264854, 2399207, 4557831, 8675836, 16544234, 31587644, 60382450, 115601178, 221625505, 425313967

Offset: 1

Author

N. J. A. Sloane, Mar 24 2002

Keywords

• nonn

Crossrefs

Cf. A025591 for middle coefficient.

Programs

PARI

a(n) = polcoeff(prod(k=1, n, 1+x^k), n*(n+1)\4 - 1); \\ Michel Marcus, Jan 04 2021