OFFSET
1,17
COMMENTS
Mir, Rosselló, and Rotger, define the cophenetic value of a pair of childless vertices as the depth (distance down from the root) of their deepest common ancestor, and they then define the total cophenetic index of a tree as the sum of the cophenetic values over all such pairs.
a(n) = 0 iff n is in A325663, being rooted stars with any arm lengths, since the root (depth 0) is the common ancestor of every childless pair.
An identity relating the childless terminal Wiener index TW(n) = A348959(n) can be constructed by noting it measures distances from a pair of childless vertices to their common ancestor, and the cophenetic values measure from that ancestor up to the root. So 2*a(n) + TW(n) is total depths Ext(n) = A196048(n) of the childless vertices, repeated by childless vertices C(n) = A109129(n) except itself, so that 2*a(n) + TW(n) = Ext(n)*(C(n) - 1)
LINKS
Arnau Mir, Francesc Rosselló, and Lucía Rotger, A New Balance Index for Phylogenetic Trees, arXiv:1202.1223 [q-bio.PE], 2012.
Kevin Ryde, PARI/GP Code
FORMULA
EXAMPLE
For n=111, the tree and its childless pairs and deepest common ancestors are
root R pair ancestor depth
/ \ G,D A 1
A B G,E A 1
/|\ \ D,E A 1
C D E F any,F R 0
| ---
G total a(n) = 3
PROG
(PARI) See links.
CROSSREFS
KEYWORD
nonn
AUTHOR
Kevin Ryde, Mar 16 2022
STATUS
approved