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 A046421 #35 Feb 16 2025 08:32:39 %S A046421 1,2,3,13,8,6,15,12,28,18,24,32,36,30,54,42,78,100,72,176,60,208,84, %T A046421 132,160,198,120,204,216,308,168,280,306,180,210,264,270,252,378,336, %U A046421 300 %N A046421 Index of smallest repunit having exactly n prime factors (counted with multiplicity). %C A046421 a(40) = 300; all other subsequent terms are > 322. - _Ray Chandler_, Apr 23 2017 %C A046421 a(41) <= 684, a(42) <= 546, a(43) <= 528, a(44) <= 462, a(45) = 360, a(46) <= 576, a(47) <= 624, a(48) <= 768. - _Daniel Suteu_, Jan 21 2023 %H A046421 Patrick De Geest, <a href="http://www.worldofnumbers.com/repunits.htm">Repunits prime factors</a> %H A046421 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Repunit.html">Repunit</a> %e A046421 For n = 5: R_6 = 111111 = 3*7*11*13*37 is the smallest repunit with five prime factors, so a(5) = 6. %o A046421 (PARI) a(n) = my(k=1); while(bigomega((10^k - 1)/9) !=n, k++); k; \\ _Michel Marcus_, Apr 23 2017 %Y A046421 Cf. A000042, A001222, A002275, A004022, A046053. %Y A046421 Initial terms of A004023, A046413, A046414, A046415, A046416, A046417, A046418, A046419. %Y A046421 Cf. A086565 (equivalent with distinct prime factors). %K A046421 nonn,more %O A046421 0,2 %A A046421 _Patrick De Geest_, Jul 15 1998 %E A046421 a(1) = 2 inserted and a(19)-a(37) added by _Ray Chandler_, Apr 23 2017 %E A046421 a(38)-a(40) from _Jinyuan Wang_, Apr 17 2020 %E A046421 Name corrected by _Felix Fröhlich_, Jun 04 2022