a(n) = ceiling(log_2 n!).

Terms

a(0) =0a(1) =0a(2) =1a(3) =3a(4) =5a(5) =7a(6) =10a(7) =13a(8) =16a(9) =19a(10) =22a(11) =26a(12) =29a(13) =33a(14) =37a(15) =41a(16) =45a(17) =49a(18) =53a(19) =57a(20) =62a(21) =66a(22) =70a(23) =75a(24) =80a(25) =84a(26) =89a(27) =94a(28) =98a(29) =103