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 A213311 #9 Jul 16 2015 22:16:00 %S A213311 103,107,111,112,115,119,122,125,129,130,134,136,138,143,147,151,152, %T A213311 155,159,163,170,174,176,178,183,191,192,195,199,202,203,205,207,212, %U A213311 215,219,220,221,224,226,228,242,245,250 %N A213311 Numbers with exactly 4 nonprime substrings (substrings with leading zeros are considered to be nonprime). %C A213311 The sequence is finite. Proof: Each 6-digit number has at least 4 nonprime substrings, and each 4-digit number has at least 1 nonprime substring. Thus, each 10-digit number has at least 5 nonprime substrings. Consequently, there is a boundary b, such that all numbers >= b have more than 4 nonprime substrings. %C A213311 The first term is a(1)=103=A213302(4). The last term is a(653)=373379=A213300(4). %H A213311 Hieronymus Fischer, <a href="/A213311/b213311.txt">Table of n, a(n) for n = 1..653</a> %e A213311 a(1) = 103, since 103 has 4 nonprime substrings (0, 03, 1, 10). %e A213311 a(653) = 373379, since there are 4 nonprime substrings (9, 33, 3379, 7337). %Y A213311 Cf. A019546, A035232, A039996, A046034, A069489, A085823, A211681, A211682, A211684, A211685. %Y A213311 Cf. A035244, A079307, A213300 - A213321. %K A213311 nonn,fini,base %O A213311 1,1 %A A213311 _Hieronymus Fischer_, Aug 26 2012