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 A098840 #16 Mar 14 2025 09:50:49
%S A098840 378,666,861,2556,5253,7503,10296,16653,27261,28920,29890,32896,46056,
%T A098840 72771,84255,85905,92235,94395,120786,132870,141778,157641,215496,
%U A098840 328455,345696,385881,386760,396495,424581,529935,533028,588070,654940
%N A098840 Smith triangular numbers.
%H A098840 Amiram Eldar, <a href="/A098840/b098840.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from Harvey P. Dale)
%H A098840 Shyam Sunder Gupta, <a href="https://doi.org/10.1007/978-981-97-2465-9_3">Triangular Numbers</a>, Exploring the Beauty of Fascinating Numbers, Springer (2025) Ch. 3, 83-125. See also <a href="https://doi.org/10.1007/978-981-97-2465-9_4">Smith Numbers</a>, Ch. 4, 127-157.
%e A098840 a(1) = 378 because 378 is a Smith number as well as a triangular number.
%t A098840 Rest[Select[Accumulate[Range[1500]],!PrimeQ[#]&&Total[IntegerDigits[#]] == Total[Flatten[ IntegerDigits/@Flatten[Table[#[[1]],{#[[2]]}]&/@ FactorInteger[ #]]]]&]] (* _Harvey P. Dale_, Oct 20 2012 *)
%Y A098840 Intersection of A000217 and A006753.
%K A098840 base,nonn
%O A098840 1,1
%A A098840 _Shyam Sunder Gupta_, Oct 10 2004