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 A247906 #9 Oct 17 2014 23:38:22
%S A247906 561,286,341,781,1105,1105,133,364,703,793,1105,1099,1891,6541,1271,
%T A247906 3991,1649,1849,3059,7363,2047,1738,4537,1128,3145,2993,5365,4069,
%U A247906 4097,7421,2465,11305,2937,16589,4495,2044,6601,26885,13073,6892,22945,3885,8695,10879
%N A247906 a(n) = n-th pseudoprime to base n.
%e A247906 a(2) = A001567(2) = 561.
%e A247906 a(3) = A005935(3) = 286.
%o A247906 (PARI) for(n=2, 20, i=0; forcomposite(c=2, 1e9, if(Mod(n, c)^(c-1)==1, i++; if(i==n, print1(c, ", "); i=0; break({1}))); if(c==1e9, print1(">1e9, "))))
%Y A247906 Cf. A007535, A098650.
%Y A247906 Cf. Pseudoprimes to base b: A001567 (b=2), A005935 (b=3), A020136 (b=4), A005936 (b=5), A005937 (b=6), A005938 (b=7), A020137 (b=8), A020138 (b=9).
%K A247906 nonn
%O A247906 2,1
%A A247906 _Felix Fröhlich_, Sep 26 2014