Number of Rooted and Unrooted Trees

Number of unrooted trees for n taxa N_u=(2n-5)*(2n-7)*...*3*1=(2n-5)!/[2^n-3*(n-3)!]

Number of rooted trees for n taxa N_r=(2n-3)*(2n-5)*(2n-7)*...*3*1=(2n-3)!/[2^n-2*(n-2)!]

Note that the number of unrooted trees for n sequences is equal for the number of rooted trees for (n-1) sequences.

For comparison the universe contains only about 10⁸⁹ protons and has an age of about 5*10¹⁷ seconds or 5*10²⁹ picoseconds.