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 A179279 #27 Jul 12 2021 03:32:24
%S A179279 4,28,40,343,10744,18506,18658,22360,34486,289912,293710,565213,
%T A179279 722765,2469287,13231942,86523219
%N A179279 Composite numbers k such that (Bell(k+1) - Bell(k)) mod k = 1.
%C A179279 The congruence is true for all primes k. Bell(k) is the sequence A000110. Tested up to k=5000.
%C A179279 a(10) > 73000. - _Giovanni Resta_, Aug 26 2018
%C A179279 a(17) > 10^8. - _Hiroaki Yamanouchi_, Sep 01 2018
%C A179279 One could compute the Bell numbers mod lcm(1, 2, ..., k) (see A003418) (or even the lcm of the composite numbers up to k) to reduce the number of digits and still find the same terms. - _David A. Corneth_, Aug 26 2018
%e A179279 For k=4, (Bell(5) - Bell(4)) mod 4 = (52 - 15) mod 4 = 37 mod 4 = 1, but 4 is not prime, so 4 is a term.
%t A179279 fQ[n_] := ! PrimeQ@n && Mod[BellB[n + 1] - BellB[n], n] == 1; k = 1; lst = {}; While[k < 9201, If[fQ@k, AppendTo[lst, k]; Print@k]; k++ ]; lst (* _Robert G. Wilson v_, Jul 28 2010 *)
%Y A179279 Cf. A000110, A003418.
%K A179279 nonn,more
%O A179279 1,1
%A A179279 _Jean-Claude Arbaut_, Jul 08 2010
%E A179279 a(5)-a(9) from _Giovanni Resta_, Aug 26 2018
%E A179279 a(10)-a(16) from _Hiroaki Yamanouchi_, Sep 01 2018