OFFSET
1,2
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..100
B. M. Schein and B. Teclezghi, Endomorphisms of finite full transformation semigroups, Proc. Amer. Math. Soc., 126 (1998) 2579-2587.
PROG
(PARI) a(n)=if(n<5, return([1, 7, 40, 345][n])); n!*(sum(m=1, n, m^(n-m)*sum(k=0, (m-1)\2, sum(r=1, m-2*k, r^(m-k-r)/(m-2*k-r)!/r!)/2^k/k!)/(n-m)!)+1) \\ Charles R Greathouse IV, May 31 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
James Mitchell, May 31 2013
EXTENSIONS
a(10)-a(20) from Charles R Greathouse IV, May 31 2013
STATUS
approved