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 A078256 #10 Sep 21 2024 19:18:54
%S A078256 0,1,3,6,10,15,21,28,36,45,55,66,78,91,105,120,136,153,190,210,231,
%T A078256 253,276,325,351,378,406,435,465,496,528,561,630,666,703,741,780,820,
%U A078256 861,903,946,1035,1275,1326,1378,1485,1540,1596,1653,1830,1953,2016,2145
%N A078256 Triangular numbers in which frequency of occurrence of every digit is same.
%H A078256 Andrew Howroyd, <a href="/A078256/b078256.txt">Table of n, a(n) for n = 1..10000</a>
%t A078256 T[n_] := n*(n + 1)/2;f[n_] := Block[{dc = DigitCount[n], s},s = Select[dc, Positive];Min @@ s == Max @@ s];Select[Array[T, 70, 0], f] (* _Ray Chandler_, May 11 2007 *)
%o A078256 (PARI) \\ here isok(k) tests if each digit k has equal frequency.
%o A078256 isok(k)={my(f=vector(10)); foreach(digits(k), t, f[1+t]++); my(c=vecmax(f)); 0==#select(t->t>0&&t<c, f)}
%o A078256 lista(n)={my(L=List(), k=0); while(#L<n, my(t=k*(k+1)/2); if(isok(t), listput(L,t)); k++); Vec(L)} \\ _Andrew Howroyd_, Sep 21 2024
%Y A078256 Cf. A052046, A082646.
%K A078256 base,easy,nonn
%O A078256 1,3
%A A078256 _Amarnath Murthy_, Nov 24 2002
%E A078256 Offset changed by _Andrew Howroyd_, Sep 21 2024