OFFSET
0,3
FORMULA
a(n) = [x^n] (sqrt(x + 1)*(1 - 2*x) + sqrt(1 - 3*x)) / (sqrt(x + 1)*(1 - 4*x) + sqrt(1 - 3*x)).
a(n) = ((36-12*n)*a(n-4) + (30-14*n)*a(n-3) + (3*n-3)*a(n-2) + (4*n-3)*a(n-1))/n for n >= 5.
MAPLE
ogf := (sqrt(x + 1)*(1 - 2*x) + sqrt(1 - 3*x)) / (sqrt(x + 1)*(1 - 4*x) + sqrt(1 - 3*x)): ser := series(ogf, x, 32): seq(coeff(ser, x, n), n = 0..28);
# Alternatively:
a := proc(n) option remember; ifelse(n < 5, [1, 1, 3, 9, 28][n + 1],
((36-12*n)*a(n-4) + (30-14*n)*a(n-3) + (3*n-3)*a(n-2) + a(n-1)*(4*n-3))/n) end:
seq(a(n), n = 0..28);
CROSSREFS
KEYWORD
nonn
AUTHOR
Peter Luschny, Oct 29 2022
STATUS
approved