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

0,1

Links

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

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

Prog

(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

Crossrefs

Cf. A349813, A349814.

Sequence in context: A284619 A147549 A177355 * A076157 A087493 A118125

Adjacent sequences: A349816 A349817 A349818 * A349820 A349821 A349822

Keyword

nonn

Author

N. J. A. Sloane, Dec 24 2021

Extensions

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

Status

approved