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A349819
Central column (ignoring the zeros) of A349813, or leading entries in rows of A349814.
3
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
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
Sequence in context: A284619 A147549 A177355 * A076157 A087493 A118125
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