E.g.f. exp(x+x^2+x^4).

Terms

a(0) =1a(1) =1a(2) =3a(3) =7a(4) =49a(5) =201a(6) =1411a(7) =7183a(8) =68097a(9) =453169a(10) =4523491a(11) =34273911a(12) =403454833a(13) =3618761017a(14) =45157828899a(15) =445900023871