a(n) = 8 + floor((2 + Sum_{j=1..n-1} a(j))/4).

Terms

a(0) =8a(1) =10a(2) =13a(3) =16a(4) =20a(5) =25a(6) =31a(7) =39a(8) =49a(9) =61a(10) =76a(11) =95a(12) =119a(13) =149a(14) =186a(15) =232a(16) =290a(17) =363a(18) =454a(19) =567a(20) =709a(21) =886a(22) =1108a(23) =1385a(24) =1731a(25) =2164a(26) =2705a(27) =3381a(28) =4226a(29) =5283