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 A247606 #27 Dec 23 2024 14:53:44 %S A247606 1,7,15,36,31,62,59,111,161,113,224,175,155,258,370,358,240,436,346, %T A247606 297,557,504,691,806,477,367,554,489,938,1743,786,959,725,1526,669, %U A247606 1215,1207,1022,1359,1286,958,1947,773,1206,1328,3078,2740,1165,915,1459,1787 %N A247606 Number of non-semiprimes among "preprimes" of the n-th kind (defined in comment in A247395). %C A247606 One can prove that non-semiprimes we can find among preprimes of the n-th kind only with the smallest prime divisor 2,3,...,prime(n), where n=1 corresponds to A156759, n=2 corresponds to A247393, n=3 corresponds to A247394, etc. For example, for n=1, only among even numbers of A156759; for n=2 - only among even numbers and numbers with the smallest prime divisor 3 of A247393, etc. Thus, for every n>=1, among preprimes of the n-th kind almost all numbers are semiprimes. %H A247606 Vladimir Shevelev, <a href="https://web.archive.org/web/*/http://list.seqfan.eu/oldermail/seqfan/2014-September/013643.html">A classification of the positive integers over primes</a> %Y A247606 Cf. A156759, A247393, A247394, A247395, A247396, A247509, A247510, A247511. %K A247606 nonn %O A247606 1,2 %A A247606 _Vladimir Shevelev_, Sep 22 2014 %E A247606 More terms from _Peter J. C. Moses_, Sep 22 2014