This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A068071 #6 Feb 12 2021 06:15:13
%S A068071 1,3,6,10,55,66,210,253,666,780,4851,8911,15400,17766,125751,303810,
%T A068071 407253,906531,1125750,2648451,5925403,6706953,15772536,22207780,
%U A068071 50085036,78406503,438094800,1623331710,1764803755,3437158416
%N A068071 Triangular numbers that remain triangular when the least significant digit is moved to the beginning.
%e A068071 8911 = A000217(133) is in the sequence because 8911 becomes 1891 which is A000217(61).
%t A068071 Do[k = FromDigits[ RotateRight[ IntegerDigits[n(n + 1)/2]]]; l = Floor[ Sqrt[2k]]; If[k == l(l + 1)/2, Print[n(n + 1)/2]], {n, 1, 10^5}]
%Y A068071 Cf. A000217, A067269.
%K A068071 base,nonn
%O A068071 1,2
%A A068071 _Robert G. Wilson v_, Feb 28 2002