a(n) = ceiling(24(2^n-1)/n).

Terms

a(0) =24a(1) =36a(2) =56a(3) =90a(4) =149a(5) =252a(6) =436a(7) =765a(8) =1363a(9) =2456a(10) =4467a(11) =8190a(12) =15122a(13) =28086a(14) =52428a(15) =98303a(16) =185042a(17) =349524a(18) =662258a(19) =1258290a(20) =2396744a(21) =4575604a(22) =8753330a(23) =16777215a(24) =32212254a(25) =61946643a(26) =119304647a(27) =230087533