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 A228613 #22 Jun 02 2025 08:37:29
%S A228613 3,29,53,3,59,97,3,23,7,3,31,19,3,5,51131,3,5,2003,3,229,139,3,
%T A228613 4215399123059,5,3,179,5,3,43,7,3,103993,61141,3,19961719,13,3,
%U A228613 2391083871204802979,331,3,89,30707,3,5,601,3,5
%N A228613 Least prime factor of (2n+1)^(2n+1)+2.
%C A228613 Suggested by S. Sykora in a discussion in the OEIS users group on LinkedIn, since the numbers to be factored here are more "elementary" than those of the existing A216146, in turn motivated by A160360.
%C A228613 As of today, a(47) seems not yet known.
%H A228613 Factor DB, <a href="http://factordb.com/index.php?query=(2*n%2B1)^(2*n%2B1)%2B2">(2*n+1)^(2*n+1)+2</a>.
%F A228613 a(3k)=3 for all k >= 0.
%t A228613 Table[FactorInteger [((2 n + 1)^(2 n + 1) + 2)][[1, 1]], {n, 0, 46}] (* _Vincenzo Librandi_, Feb 24 2014 *)
%t A228613 FactorInteger[#^#+2][[1,1]]&/@Range[1,91,2] (* _Harvey P. Dale_, Aug 27 2023 *)
%o A228613 (PARI) A228613=n->factor((2*n+1)^(2*n+1)+2)[1,1]
%Y A228613 Cf. A216146, A160360.
%K A228613 nonn
%O A228613 0,1
%A A228613 _M. F. Hasler_ and _Stanislav Sykora_, Feb 22 2014