Number of parallel permutations of length n.

Terms

a(0) =0a(1) =2a(2) =8a(3) =26a(4) =82a(5) =262a(6) =856a(7) =2858a(8) =9722a(9) =33590a(10) =117570a(11) =416022a(12) =1485798a(13) =5348878a(14) =19389688a(15) =70715338a(16) =259289578a(17) =955277398a(18) =3534526378a(19) =13128240838a(20) =48932534038a(21) =182965127278a(22) =686119227298