OFFSET
1,2
COMMENTS
a(n) = A037453(2*n-1) (proved by Schur, see link).
LINKS
W. Shur, The last digit of C(2*n,n) and Sigma C(n,i)*C(2*n-2*i,n-i), The Electronic Journal of Combinatorics, #R16, Volume 4, Issue 2 (1997).
FORMULA
a(n)=2*n - 1 + 2*sum{i=1,n} 5^(i-1)*floor((2*n-1)/3^i).
PROG
(PARI) lista(nb) = {for (n=1, nb, if (sum(i=1, n, binomial(n, i)*binomial(2*n-2*i, n-i)) % 5 != 0, print1(n, ", ")); ); }
(PARI) a(n) = {2*n-1+2*sum(i=1, n, 5^(i-1)*floor((2*n-1)/3^i))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Oct 28 2012
STATUS
approved