TREE sequence

a

ab

abc

abcd

abcde

abcdef

abcdefg

abcdefgh

abcdefghi

abcdefghij

abcdefghijk

abcdefghijkl

abcdefghijklm

abcdefghijklmn

abcdefghijklmno

abcdefghijklmnop

abcdefghijklmnopq

abcdefghijklmnopqr

abcdefghijklmnopqrs

abcdefghijklmnopqrst

abcdefghijklmnopqrstu

abcdefghijklmnopqrstuv

abcdefghijklmnopqrstuvw

abcdefghijklmnopqrstuvwx

abcdefghijklmnopqrstuvwxy

abcdefghijklmnopqrstuvwxyzTREE数列