Number of palindromes (in base 7) below 7^n.

Terms

a(0) =6a(1) =12a(2) =54a(3) =96a(4) =390a(5) =684a(6) =2742a(7) =4800a(8) =19206a(9) =33612a(10) =134454a(11) =235296a(12) =941190a(13) =1647084a(14) =6588342a(15) =11529600a(16) =46118406a(17) =80707212a(18) =322828854a(19) =564950496a(20) =2259801990a(21) =3954653484a(22) =15818613942a(23) =27682574400a(24) =110730297606a(25) =193778020812a(26) =775112083254