OFFSET
1,3
COMMENTS
A tanglegram is a pair of trees with their leaves superimposed. The original tanglegram sequence (A258620) used rooted binary trees. This variation uses planted series-reduced trees.
EXAMPLE
Two of the 5 tanglegrams for a(3) are illustrated (A,B are the roots of the trees and o marks the leaves that are shared between the two trees)
A A
/ \ / \
/ / \ / / \
o o o o o o
\ | / \ / /
\ | / \ /
B B
PROG
(PARI) \\ See links in A339645 for combinatorial species functions.
seriesReducedTrees(n)={my(v=vector(n)); v[1]=sv(1); for(n=2, #v, v[n] = polcoef( sExp(x*Ser(v[1..n])), n )); x*Ser(v)}
NumUnlabeledObjsSeq(sCartPower(seriesReducedTrees(15), 2))
CROSSREFS
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Jan 01 2021
STATUS
approved