Sum_{n>=0} a(n)/10^n = exp(1).

Terms

a(0) =2a(1) =6a(2) =10a(3) =16a(4) =19a(5) =34a(6) =37a(7) =44a(8) =38a(9) =43a(10) =47a(11) =70a(12) =52a(13) =63a(14) =68a(15) =56a(16) =82a(17) =92a(18) =106a(19) =83a(20) =96a(21) =90a(22) =92a(23) =95a(24) =124a(25) =122a(26) =116a(27) =97a(28) =130a(29) =123