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 A048362 #21 Mar 07 2025 07:52:59 %S A048362 12,59,381,3684,8692,70381,122292,3762381,7453707,18856074,124721736, %T A048362 587838545,3996943276,18845571218,27483805332,394393554074, %U A048362 1246890354231,11642661866667,88292437929618,184774336842416,1158255177391940,5962836170393707,37870196138329618,59623111421253050,107479087154457892 %N A048362 a(n) is the index of the smallest triangular number containing exactly n 7's. %H A048362 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TriangularNumber.html">Triangular Number</a> %t A048362 nsmall = Table[Infinity, 20]; %t A048362 For[i = 0, i <= 10^6, i++, p = PolygonalNumber[i]; %t A048362 n0 = Count[IntegerDigits[p], 7]; %t A048362 If[nsmall[[n0]] > i, nsmall[[n0]] = i]]; %t A048362 ReplaceAll[nsmall, Infinity -> "?"] (* _Robert Price_, Mar 22 2020 *) %Y A048362 Cf. A036524, A048352, A048355, A048356, A048357, A048358, A048359, A048360, A048361, A048363, A048364, A048543. %K A048362 nonn,base %O A048362 1,1 %A A048362 _Patrick De Geest_, Mar 15 1999 %E A048362 a(13)-a(15) from _Lars Blomberg_, May 16 2011 %E A048362 a(16)-a(18) from _Giovanni Resta_, Oct 30 2019 %E A048362 a(19)-a(25) from _Max Alekseyev_, Mar 07 2025