Sum of distinct orders of degree-n even permutations.

Terms

a(0) =1a(1) =1a(2) =4a(3) =6a(4) =11a(5) =15a(6) =28a(7) =43a(8) =74a(9) =103a(10) =148a(11) =213a(12) =296a(13) =476a(14) =679a(15) =990a(16) =1133a(17) =1707a(18) =2225a(19) =3260a(20) =4591a(21) =6042a(22) =7343a(23) =9374a(24) =13774a(25) =18262a(26) =25244a(27) =30379a(28) =39768a(29) =47295