a(n) = 25*2^(n+3) - (198+392*n/3+36*n^2+10*n^3/3).

Terms

a(0) =2a(1) =32a(2) =170a(3) =596a(4) =1690a(5) =4232a(6) =9802a(7) =21580a(8) =45946a(9) =95680a(10) =196362a(11) =399172a(12) =806490a(13) =1623096a(14) =3258570a(15) =6532092a(16) =13082042a(17) =26185200a(18) =52395146a(19) =104819060a(20) =209671322a(21) =419380712a(22) =838804810a(23) =1677658796a(24) =3355373050a(25) =6710808352a(26) =13421686282a(27) =26843450020a(28) =53686985946