OFFSET
0,4
COMMENTS
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..500
Michel Bousquet and Cédric Lamathe, On symmetric structures of order two, Discrete Math. Theor. Comput. Sci. 10 (2008), 153-176. See Table 1.
FORMULA
From Andrew Howroyd, Feb 08 2024: (Start)
a(2n) = binomial(11*n,n)/(10*n+1); a(2n+1) = binomial(11*n+5,n)*6/(10*n+6).
G.f. satisfies: A(x) = 1 + x*A(x)^6*A(-x)^5. (End)
PROG
(PARI) a(n)={my(m=n\2, p=5*(n%2)+1); binomial(11*m+p-1, m)*p/(10*m+p)} \\ Andrew Howroyd, Feb 08 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jul 12 2011
EXTENSIONS
a(11) onwards from Andrew Howroyd, Jan 26 2024
a(0)=1 prepended by Andrew Howroyd, Feb 08 2024
STATUS
approved