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 A080469 #23 Nov 14 2015 15:05:22
%S A080469 36,57,121,132,552,8397,7000713,9692541,36294723,564033861
%N A080469 Composite n such that binomial(3*n,n)==3^n (mod n).
%C A080469 If p is prime, binomial(3*p,p)==3^p (mod p)
%C A080469 No other terms below 10^9.
%C A080469 A subsequence of A109641. The terms a(n) with n=2, 6, 7, 8, 9, 10 are of the form 3^k*p where p is prime and k=1, 3, 2, 5, 6, 7, respectively. It is tempting to conjecture that there are (infinitely many?) more terms of that form. - _M. F. Hasler_, Nov 11 2015
%H A080469 Max Alekseyev, <a href="http://home.gwu.edu/~maxal/gpscripts/">PARI scripts for various problems</a>
%e A080469 57 is a term because binomial(3*57, 57) = 12039059761216294940321619222324879408784636200 mod 57 = 27 == 3^57 mod 57.
%t A080469 Do[If[ !PrimeQ[n], k = Binomial[3*n, n]; m = 3^n; If[Mod[k, n] == Mod[m, n], Print[n]]], {n, 1, 70000}] (* _Ryan Propper_, Aug 12 2005 *)
%o A080469 (PARI) forcomposite(n=1,1e9, binomod(3*n,n,n)==Mod(3,n)^n && print1(n",")) \\ Cf. Alekseyev link. - _M. F. Hasler_, Nov 14 2015
%Y A080469 Cf. A109641, A109642; A109760, A109769.
%K A080469 nonn,more,hard
%O A080469 1,1
%A A080469 _Benoit Cloitre_, Oct 15 2003
%E A080469 One more term a(6) from _Ryan Propper_, Aug 12 2005
%E A080469 Four new terms a(7)-a(10) added by _Max Alekseyev_, Nov 05 2009