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 A296653 #16 Dec 14 2022 09:06:51 %S A296653 18,26432,3066830,348933114,44690978122,6553736049264 %N A296653 a(n) is the smallest k > 15 such that the density of semiprimes in 1..k is 1/n. %C A296653 The condition that k > 15 is included in the definition because the ratio (number of semiprimes in 1..k)/k is 0 for k < 4 and reaches its maximum value (2/5) only at k = 10 (the 4th semiprime) and at k = 15 (the 6th semiprime), and decreases (although not monotonically) beyond that. %F A296653 a(n) = exp(n log n + n log log n + O(n)). - _Charles R Greathouse IV_, Dec 14 2022 %e A296653 For k > 15, the ratio (number of semiprimes in 1..k)/k first decreases to -- %e A296653 1/3 at k = 18 (the 6th semiprime), so a(3) = 18; %e A296653 1/4 at k = 26432 (the 6608th semiprime), so a(4) = 26432. %Y A296653 Cf. A001358, A066265, A106130. %K A296653 nonn,more %O A296653 3,1 %A A296653 _Jon E. Schoenfield_, Dec 17 2017 %E A296653 a(7)-a(8) from _Giovanni Resta_, Aug 18 2018