OFFSET
0,2
COMMENTS
Also the number of binary words with 4n 1's and 4 0's such that for every prefix the number of 1's is >= the number of 0's. The a(1) = 14 words are: 10101010, 10101100, 10110010, 10110100, 10111000, 11001010, 11001100, 11010010, 11010100, 11011000, 11100010, 11100100, 11101000, 11110000.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..1000
Wikipedia, Young tableau
Index entries for linear recurrences with constant coefficients, signature (5,-10,10,-5,1).
FORMULA
G.f.: (3*x^4-15*x^3-25*x^2-205*x-14)*x/(x-1)^5.
a(n) = (4*n-3)*(4*n+3)*(2*n+1)*(n+1)/3 for n>0, a(0) = 0.
MAPLE
a:= n-> max(0, (4*n+3)*(2*n+1)*(4*n-3)*(n+1)/3):
seq(a(n), n=0..40);
MATHEMATICA
LinearRecurrence[{5, -10, 10, -5, 1}, {0, 14, 275, 1260, 3705, 8602}, 40] (* Harvey P. Dale, Jan 25 2024 *)
PROG
(PARI) a(n)=max((4*n-3)*(4*n+3)*(2*n+1)*(n+1)/3, 0) \\ Charles R Greathouse IV, Oct 21 2022
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Alois P. Heinz, Aug 15 2012
STATUS
approved