OFFSET
1,1
LINKS
B. Fontaine and P.-G. Plamondon, Counting friezes in type D_n, arXiv:1409.3698 [math.CO], 2014.
FORMULA
a(n) = sum_{m=1..floor(sqrt(n+1))} binomial(2n-m^2+1,n).
PROG
(PARI) a(n) = sum(m=1, sqrtint(n+1), binomial(2*n-m^2+1, n) ); \\ Joerg Arndt, Sep 16 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Bruce Fontaine, Sep 16 2014
STATUS
approved