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

Terms

a(0) =0a(1) =1a(2) =7a(3) =19a(4) =39a(5) =71a(6) =123a(7) =211a(8) =367a(9) =655a(10) =1203a(11) =2267a(12) =4359a(13) =8503a(14) =16747a(15) =33187a(16) =66015a(17) =131615a(18) =262755a(19) =524971a(20) =1049335a(21) =2097991a(22) =4195227a(23) =8389619a(24) =16778319a(25) =33555631a(26) =67110163a(27) =134219131a(28) =268436967a(29) =536872535