a(n)=sum(k=1,n,C(n,n reduced (mod k))).

Terms

a(0) =1a(1) =2a(2) =5a(3) =7a(4) =22a(5) =25a(6) =79a(7) =124a(8) =276a(9) =444a(10) =1267a(11) =1657a(12) =4435a(13) =7753a(14) =17327a(15) =28309a(16) =72728a(17) =110949a(18) =279663a(19) =476090a(20) =1071672a(21) =1834419a(22) =4512625a(23) =7194685a(24) =17326148a(25) =30229021a(26) =68385742a(27) =117709413a(28) =280395840a(29) =466385404