a(n) = Sum_{d|n} Stirling2(n,d).

Terms

a(0) =1a(1) =2a(2) =2a(3) =9a(4) =2a(5) =123a(6) =2a(7) =1830a(8) =3027a(9) =43038a(10) =2a(11) =2023728a(12) =2a(13) =49337473a(14) =213142023a(15) =2313595723a(16) =2a(17) =216927216877a(18) =2a(22) =2a(28) =2