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 A048358 #21 Mar 07 2025 07:45:54 %S A048358 2,77,257,2570,816,25808,163299,812816,2463060,24629808,246306030, %T A048358 791999183,812812816,2581876578,81649658057,247924719918,812812812816, %U A048358 8128140492564,25819877355763,81708543315045,816129320553227,2581981926944235,8164822512869870,16329935292787435,258071204644507494 %N A048358 a(n) is the index of the smallest triangular number containing exactly n 3's. %H A048358 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TriangularNumber.html">Triangular Number</a> %t A048358 nsmall = Table[Infinity, 20]; %t A048358 For[i = 0, i <= 10^6, i++, p = PolygonalNumber[i]; %t A048358 n0 = Count[IntegerDigits[p], 3]; %t A048358 If[nsmall[[n0]] > i, nsmall[[n0]] = i]]; %t A048358 ReplaceAll[nsmall, Infinity -> "?"] (* _Robert Price_, Mar 22 2020 *) %Y A048358 Cf. A036520, A048348, A048355, A048356, A048357, A048359, A048360, A048361, A048362, A048363, A048364, A048535. %K A048358 nonn,base %O A048358 1,1 %A A048358 _Patrick De Geest_, Mar 15 1999 %E A048358 a(12) corrected by _Lars Blomberg_, May 13 2011 %E A048358 a(13)-a(15) from _Lars Blomberg_, May 13 2011 %E A048358 a(16)-a(18) from _Giovanni Resta_, Oct 30 2019 %E A048358 a(19)-a(25) from _Max Alekseyev_, Mar 07 2025