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 A066569 #16 May 21 2022 19:41:50
%S A066569 1,3,6,55,66,153,171,351,595,666,3003,5995,8778,15051,17578,66066,
%T A066569 87571,185745,547581,617716,828828,1269621,1461195,1680861,3544453,
%U A066569 5073705,5676765,5911641,6295926,12145056,12517506,35133153,60571521
%N A066569 Triangular numbers whose reverse is also triangular.
%C A066569 Numbers ending in 0 are not included. - _Harry J. Smith_, Mar 06 2010
%H A066569 Harry J. Smith, <a href="/A066569/b066569.txt">Table of n, a(n) for n = 1..100</a>
%e A066569 153 and 351 are both triangular.
%t A066569 dtn[L_] := Fold[10#1+#2&, 0, L] tritest[n_] := Module[{t}, t=Floor[N[Sqrt[2n]]]; 2n==t(t+1)] A={}; For[i=1, i>0, i++, t=i(i+1)/2; If[tritest[dtn[Reverse[IntegerDigits[t]]]]&&Mod[t, 10]>0, AppendTo[A, t]; Print[A]]]
%t A066569 Select[Accumulate[Range[12000]],Last[IntegerDigits[#]]!=0&&OddQ[Sqrt[1+ 8*FromDigits[Reverse[IntegerDigits[#]]]]]&] (* _Harvey P. Dale_, Jun 04 2015 *)
%o A066569 (PARI) Rev(x)= { local(d, r=0); while (x>0, d=x%10; x\=10; r=r*10 + d); return(r) } { n=0; for (m=1, 10^10, t=m*(m + 1)/2; if (t%10 == 0, next); if (issquare(8*Rev(t) + 1), write("b066569.txt", n++, " ", t); if (n==100, return)) ) } \\ _Harry J. Smith_, Mar 08 2010
%Y A066569 Cf. A003098, A061455, A066528, A069673.
%K A066569 base,nonn
%O A066569 1,2
%A A066569 _Erich Friedman_, Jan 08 2002
%E A066569 Offset changed from 0 to 1 by _Harry J. Smith_, Mar 06 2010