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 A177884 #16 Oct 26 2015 22:20:22 %S A177884 1387,2047,4371,8911,13747,14491,19951,42799,60787,90751,123251, %T A177884 150851,256999,258511,271951,272251,275887,294271,387731,396271, %U A177884 422659,435671,443719,452051,476971,514447,672487,680627,741751,769567,877099,916327,1024651,1052503,1092547,1152271,1277179,1302451,1325843,1397419,1419607,1433407,1441091,1459927 %N A177884 Pseudoprimes to base 2 of the form 4k+3. %C A177884 In at least the first 1801533 values (that is, for 2-pseudoprimes <10^15) of A001567, the entries of the form 4k+3 are less numerous than those of the form 4k+1. Is this always the case? %H A177884 Charles R Greathouse IV, <a href="/A177884/b177884.txt">Table of n, a(n) for n = 1..10000</a> %F A177884 A001567 INTERSECT A004767. %o A177884 (PARI) forstep(n=3,10^7,4,if(isprime(n),next());if(Mod(2,n)^(n-1)==1,print1(n,", "))) %Y A177884 Cf. A001567, A178723. %K A177884 nonn %O A177884 1,1 %A A177884 _Juri-Stepan Gerasimov_, Dec 14 2010 %E A177884 Terms corrected by _R. J. Mathar_, Dec 17 2010