Number of palindromes (in base 4) below 4^n.

Terms

a(0) =3a(1) =6a(2) =18a(3) =30a(4) =78a(5) =126a(6) =318a(7) =510a(8) =1278a(9) =2046a(10) =5118a(11) =8190a(12) =20478a(13) =32766a(14) =81918a(15) =131070a(16) =327678a(17) =524286a(18) =1310718a(19) =2097150a(20) =5242878a(21) =8388606a(22) =20971518a(23) =33554430a(24) =83886078a(25) =134217726a(26) =335544318a(27) =536870910a(28) =1342177278a(29) =2147483646