E.g.f.: -cosh(x)*LambertW(-x).

Terms

a(0) =0a(1) =1a(2) =2a(3) =12a(4) =76a(5) =720a(6) =8766a(7) =131096a(8) =2319416a(9) =47361600a(10) =1096018330a(11) =28344108672a(12) =810053677764