a(n) = (n+1)*(2^(n+1) - n)/2.

Terms

a(0) =1a(1) =3a(2) =9a(3) =26a(4) =70a(5) =177a(6) =427a(7) =996a(8) =2268a(9) =5075a(10) =11209a(11) =24510a(12) =53170a(13) =114597a(14) =245655a(15) =524168a(16) =1113976a(17) =2359143a(18) =4980565a(19) =10485570a(20) =22019886a(21) =46137113a(22) =96468739a(23) =201326316a(24) =419430100a(25) =872414907a(26) =1811938977a(27) =3758096006a(28) =7784627818a(29) =16106126925