a(n+1) = a(n) + n (if n is odd), a(n+1) = a(n) * n (if n is even).

Terms

a(0) =1a(1) =2a(2) =4a(3) =7a(4) =28a(5) =33a(6) =198a(7) =205a(8) =1640a(9) =1649a(10) =16490a(11) =16501a(12) =198012a(13) =198025a(14) =2772350a(15) =2772365a(16) =44357840a(17) =44357857a(18) =798441426a(19) =798441445a(20) =15968828900a(21) =15968828921a(22) =351314236262a(23) =351314236285