OFFSET
1,6
COMMENTS
A rooted plane tree is series-reduced if every non-leaf node has at least two branches, and palindromic if the sequence of branches directly under any given node is a palindrome.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..500
MATHEMATICA
srpanplane[n_]:=If[n==1, {{}}, Join@@Table[Select[Tuples[srpanplane/@c], #==Reverse[#]&], {c, Join@@Permutations/@Select[IntegerPartitions[n-1], Length[#]>1&]}]];
Table[Length[srpanplane[n]], {n, 15}]
PROG
(PARI) PAL(p)={(1+p)/subst(1-p, x, x^2)}
seq(n)={my(p=O(1)); for(i=1, n, p=PAL(x*p)-x*p); Vec(p)} \\ Andrew Howroyd, Sep 19 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Sep 18 2018
EXTENSIONS
Terms a(27) and beyond from Andrew Howroyd, Sep 19 2018
STATUS
approved