a(n) = 541*(2^n - 1) - 5*n^4 - 30*n^3 - 130*n^2 - 375*n.

Terms

a(0) =1a(1) =33a(2) =277a(3) =1335a(4) =4771a(5) =14193a(6) =37417a(7) =90795a(8) =207871a(9) =456693a(10) =974437a(11) =2036655a(12) =4195771a(13) =8558073a(14) =17337697a(15) =34964595a(16) =70300471a(17) =141070653a(18) =282727837a(19) =566179575a(20) =1133243251a(21) =2267556033a(22) =4536394777a(23) =9074315835a(24) =18150434671a(25) =36302985093a(26) =72608437717a(27) =145219736895