a(0)=0, a(1)=1, a(n) = n! - a(n-2).

Terms

a(0) =0a(1) =1a(2) =2a(3) =5a(4) =22a(5) =115a(6) =698a(7) =4925a(8) =39622a(9) =357955a(10) =3589178a(11) =39558845a(12) =475412422a(13) =6187461955a(14) =86702878778