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 A000864 #34 Aug 14 2021 18:52:29
%S A000864 91,259,451,481,703,1729,2821,2981,3367,4141,4187,5461,6533,6541,6601,
%T A000864 7471,7777,8149,8401,8911,10001,11111,12403,13981,14701,14911,15211,
%U A000864 15841,19201,21931,22321,24013,24661,27613,29341,34133
%N A000864 Deceptive nonprimes: composite numbers k that divide the repunit R_{k-1}.
%C A000864 Francis and Ray call these numbers "deceptive primes".
%C A000864 Pseudoprimes to base 10, A005939, not divisible by 3. If k is in the sequence, then (10^k-1)/9 is in the sequence, by Steuerwald's theorem; see A005935. - _Thomas Ordowski_, Apr 10 2016
%C A000864 41041 is the first term that has four prime divisors. - _Altug Alkan_, Apr 10 2016
%H A000864 Charles R Greathouse IV, <a href="/A000864/b000864.txt">Table of n, a(n) for n = 1..10000</a>
%H A000864 R. Francis and T. Ray, <a href="https://doi.org/10.35834/2000/1203145">The deceptive primes to 2.10^7</a>, Missouri J. Math. Sci. 12 (2000), no. 3, 145-158.
%p A000864 select(t -> not isprime(t) and (10&^(t-1) - 1) mod (9*t) = 0, [seq(t,t=3..10^5,2)]); # _Robert Israel_, Apr 10 2016
%o A000864 (PARI) p=5;forprime(q=7,1e5,forstep(n=p+2,q-2,2,if(n%5 && Mod(10,9*n)^(n-1)==1,print1(n", ")));p=q) \\ _Charles R Greathouse IV_, Jul 31 2011
%Y A000864 Cf. A002275, A005939.
%K A000864 nonn
%O A000864 1,1
%A A000864 Tim Ray (c268scm(AT)semovm.semo.edu)