This is an analog for T_n of sequence A071605 (or A040175) for the symmetric group S_n.
P. J. Cameron, Dixon's theorem and random synchronization, Discrete Math., 313 (2013), 1233-1246. (a(1)-a(6) were computed by James Mitchell.)
Table of n, a(n) for n=1..6.
Cf. A040175, A071605.
Sequence in context: A064344 A163046 A193381 * A210816 A133415 A192602
Adjacent sequences: A224536 A224537 A224538 * A224540 A224541 A224542
N. J. A. Sloane, Apr 29 2013