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 A048361 #21 Mar 07 2025 07:52:26 %S A048361 3,11,36,363,3366,8563,35963,394123,3055048,11531588,115464831, %T A048361 115470036,1154484036,10645763163,35401884036,152754484036, %U A048361 365148371588,2292012515963,33065591380305,115470003521836,642442319075676,1154701378423588,10996978373724908,36347397889274188,230810167309875091 %N A048361 a(n) is the index of the smallest triangular number containing exactly n 6's. %H A048361 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TriangularNumber.html">Triangular Number</a> %t A048361 nsmall = Table[Infinity, 20]; %t A048361 For[i = 0, i <= 10^6, i++, p = PolygonalNumber[i]; %t A048361 n0 = Count[IntegerDigits[p], 6]; %t A048361 If[nsmall[[n0]] > i, nsmall[[n0]] = i]]; %t A048361 ReplaceAll[nsmall, Infinity -> "?"] (* _Robert Price_, Mar 22 2020 *) %Y A048361 Cf. A036523, A048351, A048355, A048356, A048357, A048358, A048359, A048360, A048362, A048363, A048364, A048541. %K A048361 nonn,base %O A048361 1,1 %A A048361 _Patrick De Geest_, Mar 15 1999 %E A048361 a(13)-a(15) from _Lars Blomberg_, May 16 2011 %E A048361 a(16)-a(18) from _Giovanni Resta_, Oct 30 2019 %E A048361 a(19)-a(25) from _Max Alekseyev_, Mar 07 2025