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 A114250 #23 Feb 16 2025 08:32:59
%S A114250 0,0,0,0,3,19,63,175,501,1230,3086,7469,18402,44748,109787,269289,
%T A114250 668521,1675317,4236270
%N A114250 Number of Fermat pseudoprimes to bases 2, 3, 5 and 7 less than 10^n.
%H A114250 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/FermatPseudoprime.html">Fermat Pseudoprime</a>.
%F A114250 a(n) = card{ m in A083739, m<10^n}. - _R. J. Mathar_, Feb 07 2008
%t A114250 Table[Count[Select[Range[2, 10^6], ! PrimeQ[#] && PowerMod[2, # - 1, #] == 1 && PowerMod[3, # - 1, #] == 1 && PowerMod[5, # - 1, #] == 1 && PowerMod[7, # - 1, #] == 1 &], x_ /; x < 10^n], {n, 6}] (* _Robert Price_, Jun 09 2019 *)
%Y A114250 Cf. A083739.
%K A114250 nonn,more
%O A114250 1,5
%A A114250 _Eric W. Weisstein_, Nov 18 2005
%E A114250 a(9)-a(12) from _Amiram Eldar_, Sep 18 2021
%E A114250 a(13)-a(19) from _Amiram Eldar_, Apr 22 2022