E.g.f.: exp(2*(1-exp(x))).

Terms

a(0) =1a(1) =-2a(2) =2a(3) =2a(4) =-6a(5) =-14a(6) =26a(7) =178a(8) =90a(9) =-2382a(10) =-9446a(11) =13746a(12) =287194a(13) =998578a(14) =-3687782a(15) =-56264782a(16) =-208446118a(17) =1017677490a(18) =17194912282a(19) =79540574642a(20) =-317691584294