OFFSET
1,3
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..100
EXAMPLE
The a(6) = 11 trees:
(((((o)))))
((((oo))))
(((ooo)))
(((o)(o)))
((oo(o)))
((oooo))
(oo((o)))
(oo(oo))
(o(o)(o))
(ooo(o))
(ooooo)
MATHEMATICA
strut[n_]:=strut[n]=If[n===1, {{}}, Select[Join@@Function[c, Union[Sort/@Tuples[strut/@c]]]/@IntegerPartitions[n-1], UnsameQ@@Length/@Split[#]&]];
Table[Length[strut[n]], {n, 10}]
PROG
(PARI)
C(v, n)={my(recurse(r, b, p, k)=if(!r, 1, sum(m=1, r, if(!bittest(b, m), sum(i=1, min(r\m, p), my(f=if(i==p, k+1, 1)); if(v[i]>=f, (v[i]-f+1)*self()(r-m*i, bitor(b, 1<<m), i, f)/f)))))); recurse(n, 0, #v, 0)}
seq(n)={my(v=vector(n)); v[1]=1; for(n=2, #v, v[n]=C(v[1..n-1], n-1)); v} \\ Andrew Howroyd, Feb 08 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jul 14 2018
EXTENSIONS
Terms a(26) and beyond from Andrew Howroyd, Feb 08 2020
STATUS
approved