For the n in S000378, the tetrahedral number n*(n+1)*(n+2)/6 in base 9.
555, 505555505, 505055555550505, 505050555555555050505, 505050505555555555505050505, 505050505055555555555550505050505, 505050505050555555555555555050505050505, 505050505050505555555555555555505050505050505
1
All these numbers are palindromic.
T. D. Noe, Plot of 100 terms
T. D. Noe, Table of 100 terms
Eric W. Weisstein, MathWorld: Tetrahedral Number
(Mma) t = Table[(3^(4*n - 1) - 1)/2, {n, 15}]; Table[FromDigits[IntegerDigits[n*(n+1)*(n+2)/6, 9]], {n, t}]
Cf. S000378.
nonn,base
T. D. Noe, Nov 23 2014