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 A140286 #16 May 10 2020 19:30:21 %S A140286 3,15,99,495,2079,4455,36855,70875,280665,1393119,4179357,12931731, %T A140286 32417901,161026623,514966329,1490692005 %N A140286 The n-th lucky number which is the product of exactly n primes (with multiplicity). %C A140286 This is the main diagonal of the infinite array A(k,n) = n-th n-th lucky number to be the product of exactly k primes, with multiplicity, which begins as below: %C A140286 ============================================================================ %C A140286 k | n=1 | n=2 | n=3 | n=4 | n=5 | n=6 | n=7 | n=8 | n=9 | n=10 |in OEIS %C A140286 1 | 3 | 7 | 13 | 31 | 37 | 43 | 67 | 73 | 79 | 127 |A031157 %C A140286 2 | 9 | 15 | 21 | 25 | 33 | 49 | 51 | 69 | 87 | 93 |A139787 %C A140286 3 | 63 | 75 | 99 | 105 | 171 | 195 | 231 | 261 | 273 | 285 | %C A140286 4 | 297 | 495 | 621 | 693 | 735 | 819 | 855 | 975 | 1029 | 1107 | %C A140286 5 | 1053 | | %C A140286 6 | 729 | | %C A140286 ============================================================================ %C A140286 a(16) > 10^9. - _Donovan Johnson_, Oct 24 2010 %e A140286 a(4) = 693 because the 113th lucky number = 693 = 3^2 * 7 * 11 is the 4th lucky number with 4 prime factors. %Y A140286 Cf. A000040, A000959, A001358, A014612, A031157, A139787. %K A140286 nonn,more,less %O A140286 1,1 %A A140286 _Jonathan Vos Post_, May 24 2008 %E A140286 a(4) corrected and 5 more terms via b000959.txt from _R. J. Mathar_, Oct 22 2010 %E A140286 a(10)-a(15) from _Donovan Johnson_, Oct 24 2010 %E A140286 a(16) from _Giovanni Resta_, May 10 2020