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 A109760 #9 Jul 28 2025 17:35:45
%S A109760 4,365,400,685,3200,6400,12550,12800,16525,25600,51200,225125,
%T A109760 70463125,271094125,431434441
%N A109760 Composite n such that binomial(5*n,n) == 5^n (mod n).
%C A109760 No other terms below 10^9.
%H A109760 Max Alekseyev, <a href="http://home.gwu.edu/~maxal/gpscripts/">PARI/GP scripts for various problems</a>
%e A109760 4 is a term because binomial(5*4, 4) = 4845, 5^4 = 625 and 4845 mod 4 = 625 mod 4 = 1.
%t A109760 Do[If[ !PrimeQ[n], If[Mod[Binomial[5*n, n], n] == Mod[5^n, n], Print[n]]], {n, 1, 50000}]
%t A109760 Select[Range[250000],CompositeQ[#]&&Mod[Binomial[5#,#],#]==PowerMod[5,#,#]&] (* The program generates the first 12 terms of the sequence. *) (* _Harvey P. Dale_, Jul 28 2025 *)
%Y A109760 Cf. A080469.
%K A109760 hard,more,nonn
%O A109760 1,1
%A A109760 _Ryan Propper_, Aug 12 2005
%E A109760 a(12) from _D. S. McNeil_, Mar 15 2009
%E A109760 225125 from _Max Alekseyev_, Sep 13 2009
%E A109760 Three more terms from _Max Alekseyev_, Nov 06 2009