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 A069077 #28 Apr 16 2025 05:25:49 %S A069077 1,3,6,66,153,231,351,465,741,1326,2556,5671,6786,14535,21115,24531, %T A069077 25651,33411,43956,57291,58311,71253,92665,95266,123753,153181,167331, %U A069077 278631,325221,341551,351541,372816,459361,491536,516636,521731,567645,572985,613278 %N A069077 Triangular numbers such that the product of digits is also a (positive) triangular number. %H A069077 Amiram Eldar, <a href="/A069077/b069077.txt">Table of n, a(n) for n = 1..457</a> %t A069077 aQ[n_] := (p = Times @@ IntegerDigits[n]) > 0 && IntegerQ @ Sqrt[8p + 1]; t[n_] := n(n+1)/2; Select[t[Range[10^3]], aQ] (* _Amiram Eldar_, Aug 12 2019 *) %t A069077 Select[Accumulate[Range[1500]],FreeQ[IntegerDigits[#],0]&&OddQ[Sqrt[8 Times@@IntegerDigits[ #]+1]]&] (* _Harvey P. Dale_, May 01 2023 *) %o A069077 (Magma) [m:m in [1..600000]|not 0 in Intseq(m) and IsSquare(8*m+1) and IsSquare(8*(&*Intseq(m))+1)]; // _Marius A. Burtea_, Aug 12 2019 %Y A069077 Cf. A000217, A002473, A007954, A061380. %K A069077 nonn,base %O A069077 1,2 %A A069077 _Amarnath Murthy_, Apr 05 2002 %E A069077 More terms from _Jason Earls_ and _Lior Manor_, May 15 2002