OFFSET
0,2
COMMENTS
O.g.f. is 1/x * the series reversion of x*(1 - x)^k/(1 + x)^(k+2) at k = 6. See the cross references for related sequences obtained from other values of k.
LINKS
FORMULA
a(n-1) = 1/n * Sum_{i = 0..n-1} binomial(8*n,i)*binomial(7*n-i-2,n-i-1).
O.g.f.: A(x) = exp ( Sum_{n >= 1} 1/n! * (8*n)!/(4*n)! * (3*n)!/(6*n)!*x^n/n ) = 1 + 14*x + 293*x^2 + 7266*x^3 + ....
1 + x*A'(x)/A(x) is the o.g.f. for A211421.
O.g.f. is the series reversion of x*(1 - x)^6/(1 + x)^8.
a(0) = 1 and for n >= 1, a(n) = 1/n * Sum {k = 1..n} 1/k! * (8*k)!/(4*k)! * (3*k)!/(6*k)!*a(n-k).
MAPLE
PROG
(PARI) a(n) = sum(k=0, n, binomial(8*(n+1), k)*binomial(7*(n+1)-k-2, (n+1)-k-1))/(n+1); \\ Altug Alkan, Oct 03 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Peter Bala, Sep 29 2015
STATUS
approved