E.g.f. cosh(x+x^2/2).

Terms

a(0) =1a(1) =0a(2) =1a(3) =3a(4) =4a(5) =10a(6) =46a(7) =126a(8) =316a(9) =1296a(10) =5356a(11) =17380a(12) =63856a(13) =296088a(14) =1264264a(15) =4940040a(16) =22302736a(17) =110455936a(18) =507711376a(19) =2313783216a(20) =11798364736a(21) =61878663840a(22) =309240315616