Denominator of a sequence of fractions converging to e.

Terms

a(0) =1a(1) =2a(2) =7a(3) =18a(4) =71a(5) =252a(6) =1001a(7) =4540a(8) =18089a(9) =99990a(10) =398959a(11) =2602278a(12) =10391023a(13) =78132152a(14) =312129649a(15) =2658297528a(16) =10622799089a(17) =101072656170a(18) =403978495031