Number of palindromes (in base 5) below 5^n.

Terms

a(0) =4a(1) =8a(2) =28a(3) =48a(4) =148a(5) =248a(6) =748a(7) =1248a(8) =3748a(9) =6248a(10) =18748a(11) =31248a(12) =93748a(13) =156248a(14) =468748a(15) =781248a(16) =2343748a(17) =3906248a(18) =11718748a(19) =19531248a(20) =58593748a(21) =97656248a(22) =292968748a(23) =488281248a(24) =1464843748a(25) =2441406248a(26) =7324218748a(27) =12207031248a(28) =36621093748a(29) =61035156248