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 A230808 #7 Oct 30 2013 21:53:47 %S A230808 3,641,643,4369,25759,33149,87249,129917,157637,212419,332947,451901, %T A230808 656597,656599,831405,1489665,1608461,2113665,3020357,3370637,6212357, %U A230808 6212359,19092917,31880577,34487597,38790749,63560683,81612105,84028407,86559045,274014885 %N A230808 Smallest sets of 3 consecutive odd numbers that are primes or pseudoprime (base 2). The initial odd number is listed. %H A230808 Shyam Sunder Gupta, <a href="/A230808/b230808.txt">Table of n, a(n) for n = 1..5001</a> %H A230808 Jan Feitsma, <a href="http://www.cecm.sfu.ca/Pseudoprimes/index-2-to-64.html">Tables of pseudoprimes and related data</a> %e A230808 641 is in sequence because 641, 643, 645 is a set of 3 consecutive odd number where 645 is pseudoprime base 2 and others are prime. %Y A230808 Cf. A001567, A230559, A228575, A230668, A230715. %K A230808 nonn %O A230808 1,1 %A A230808 _Shyam Sunder Gupta_, Oct 30 2013