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 A067269 #12 Sep 17 2024 12:34:35
%S A067269 1,3,6,10,55,66,300,325,666,1035,1485,1891,61776,103740,109746,112575,
%T A067269 190653,340725,1026028,1264845,3000025,3002475,3592540,3670695,
%U A067269 37840650,60000535,61577253,65008503,1001393128,1432436050,1560756385
%N A067269 Triangular numbers which remain triangular when the most significant digit is moved to the end.
%e A067269 1485 is a term as 1485 and 4851 both are triangular numbers.
%t A067269 Do[k = FromDigits[ RotateLeft[ IntegerDigits[n(n + 1)/2]]]; l = Floor[ Sqrt[2k]]; If[k == l(l + 1)/2, Print[n(n + 1)/2]], {n, 1, 10^5}]
%t A067269 msdmeQ[n_]:=IntegerQ[(Sqrt[1+8*FromDigits[RotateLeft[IntegerDigits[ n]]]]-1)/2]; Select[Accumulate[Range[55900]],msdmeQ] (* _Harvey P. Dale_, Aug 22 2014 *)
%Y A067269 Cf. A000217, A345110.
%K A067269 base,nonn
%O A067269 1,2
%A A067269 _Amarnath Murthy_, Feb 22 2002
%E A067269 Edited by _Robert G. Wilson v_, Feb 28 2002
%E A067269 Offset changed by _Andrew Howroyd_, Sep 17 2024