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 A254139 #12 Jul 16 2017 15:13:36
%S A254139 9,28,15,66,49,232,45,190,121,276,169,1106
%N A254139 a(n) = smallest composite c for which there exist exactly n bases b with b < c such that b^(c-1) == 1 (mod c), i.e., smallest composite c which is a Fermat pseudoprime to exactly n bases less than c.
%C A254139 a(13) > 150000.
%e A254139 With c = 49: there are exactly five bases b with b < 49 such that 49 is a Fermat pseudoprime, namely 18, 19, 30, 31 and 48. Since 49 is the smallest composite having exactly five such bases, a(5) = 49.
%o A254139 (PARI) for(n=1, 20, forcomposite(c=3, , b=2; i=0; while(b < c, if(Mod(b, c)^(c-1)==1, i++); b++); if(i==n, print1(c, ", "); break({1}))))
%Y A254139 Cf. A001567, A141768, A181780.
%K A254139 nonn,more
%O A254139 1,1
%A A254139 _Felix Fröhlich_, Jan 26 2015