a(n) = (n^n + n)/2.A117694a(n) = (n^n + n)/2.Terms a(0) =1a(1) =3a(2) =15a(3) =130a(4) =1565a(5) =23331a(6) =411775a(7) =8388612a(8) =193710249a(9) =5000000005a(10) =142655835311External referencesoeis: A117694