OFFSET
1,3
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..2680
V. Jovovic and G. Kilibarda, Enumeration of labeled quasi-initially connected digraphs, Discrete Math., 224 (2000), 151-163.
EXAMPLE
Triangle begins:
[1],
[0,2,1],
[0,0,6,20,15,6,1],
[0,0,0,0,24,222,660,908,792,495,220,66,12,1],
...
The number of unilaterally connected digraphs on 3 labeled nodes is 48 = 6+20+15+6+1.
PROG
(PARI) \\ See A057273 for Strong.
Unilaterally(n, e=2)={my(u=vector(n), s=Strong(n, e)); for(n=1, #u, u[n]=vector(n, k, binomial(n, k)*s[k]*if(k==n, 1, sum(j=1, n-k, e^(k*(n-k-j))*(e^(k*j)-1)*u[n-k][j])))); vector(#u, n, vecsum(u[n]))}
row(n)={Vecrev(Unilaterally(n, 1+'y)[n])}
{ for(n=1, 5, print(row(n))) } \\ Andrew Howroyd, Jan 19 2022
CROSSREFS
KEYWORD
nonn,tabf
AUTHOR
Vladeta Jovovic, Goran Kilibarda, Sep 14 2000
STATUS
approved