Palindromic triangular numbers in base 6.
1, 3, 33, 44, 131, 3553, 32123, 34243, 131131, 415514, 1011101, 4122214, 33111133, 41233214, 1340000431, 32153035123, 34234443243, 41540004514, 1011132311101, 3252411142523, 3522120212253, 4103111113014, 4131354531314, 31540144104513
1
See S000348 for the n that produce these triangular numbers.
T. D. Noe, Plot of 46 terms
T. D. Noe, Table of 46 terms
Eric W. Weisstein, MathWorld: Triangular Number
(Mma) ff[base_, len_] := Module[{n = 0, t = {}, tri, d}, While[Length[t] < len, n++; tri = n*(n + 1)/2; d = IntegerDigits[tri, base]; If[d == Reverse[d], AppendTo[t, n]]]; t]; t6 = ff[6, 20]; Table[FromDigits[IntegerDigits[n*(n + 1)/2, 6]], {n, t6}]
Cf. S000348.
nonn,base,hard
T. D. Noe, Nov 19 2014