Second column of PE^3.

Terms

a(0) =0a(1) =1a(2) =6a(3) =36a(4) =228a(5) =1545a(6) =11196a(7) =86457a(8) =708504a(9) =6136830a(10) =55976430a(11) =535904259a(12) =5369146272a(13) =56145107577a(14) =611336534802