A349819 Central column (ignoring the zeros) of A349813, or leading entries in rows of A349814.

3, 1, 3, 4, 20, 31, 182, 304, 1932, 3364, 22407, 40044, 275132, 500522, 3515564, 6478784, 46260604, 86094668, 622636764, 1167752848, 8531618640, 16100882359, 118615471982, 225001039696, 1669094344820, 3179713880524, 23725950404610, 45364387834120, 340192536782760

Offset: 0

Author

N. J. A. Sloane, Dec 24 2021

Keywords

• nonn

Links

• Andrew Howroyd, Table of n, a(n) for n = 0..500

Crossrefs

Cf. A349813, A349814.

Programs

PARI

a(n) = if(n==0, 3, polcoef((-3 - x + x^2 + 3*x^3)*(1 + x + x^2 + x^3)^(n-1), 3*n\2+1)) \\ Andrew Howroyd, Feb 28 2023

Formula

a(n) = [x^floor(3*n/2+1)](-3 - x + x^2 + 3*x^3)*(1 + x + x^2 + x^3)^(n-1) for n > 0. - Andrew Howroyd, Feb 28 2023

Extensions

Offset corrected and terms a(21) and beyond from Andrew Howroyd, Feb 28 2023