a(n) = floor(exp(n - gamma)), where gamma is Euler's constant.

Terms

a(0) =0a(1) =1a(2) =4a(3) =11a(4) =30a(5) =83a(6) =226a(7) =615a(8) =1673a(9) =4549a(10) =12366a(11) =33616a(12) =91380a(13) =248397a(14) =675213a(15) =1835420a(16) =4989191a(17) =13562027a(18) =36865412a(19) =100210580a(20) =272400600a(21) =740461601a(22) =2012783315a(23) =5471312310a(24) =14872568831a(25) =40427833596a(26) =109894245428