OFFSET
0,4
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..500
FORMULA
a(n) = [x^floor(3*n/2+1)](-1 - 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, 1, polcoef((-1 - x + x^2 + x^3)*(1 + x + x^2 + x^3)^(n-1), 3*n\2+1)) \\ Andrew Howroyd, Feb 28 2023
CROSSREFS
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