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A319437 Number of series-reduced palindromic plane trees with n nodes. 2
1, 0, 1, 1, 1, 2, 3, 4, 7, 10, 15, 23, 35, 52, 81, 121, 185, 280, 427, 645, 985, 1490, 2269, 3440, 5233, 7936, 12071, 18313, 27839, 42256, 64217, 97490, 148137, 224924, 341725, 518923, 788321, 1197178, 1818597, 2761926, 4195381, 6371808, 9678537, 14699771 (list; graph; refs; listen; history; text; internal format)
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
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
Sequence in context: A018132 A329758 A100638 * A270659 A159288 A363958
KEYWORD
nonn
AUTHOR
Gus Wiseman, Sep 18 2018
EXTENSIONS
Terms a(27) and beyond from Andrew Howroyd, Sep 19 2018
STATUS
approved

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Last modified May 19 23:42 EDT 2024. Contains 372703 sequences. (Running on oeis4.)