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 A078311 #12 Apr 10 2025 06:53:10 %S A078311 2,5,2,3,2,37,2,17,2,101,2,73,2,197,2,3,2,109,2,3,2,5,2,5,2,677,2,3,2, %T A078311 17,2,5,2,13,2,7,2,5,2,401,2,5,2,3,2,29,2,17,2,3,2,3,2,5,2,5,2,5,2, %U A078311 1801,2,5,2,3,2,4357,2,3,2,13,2,433,2,5477,2,3,2,5,2,3,2,5,2,3529,2,13 %N A078311 Smallest prime factor of n*rad(n)+1, where rad = A007947 (squarefree kernel). %H A078311 Reinhard Zumkeller, <a href="/A078311/b078311.txt">Table of n, a(n) for n = 1..10000</a> %F A078311 a(n) = A020639(A078310(n)). %t A078311 a[n_] := FactorInteger[1 + n * Times @@ FactorInteger[n][[;;, 1]]][[1, 1]]; Array[a, 100] (* _Amiram Eldar_, Apr 10 2025 *) %o A078311 (Haskell) %o A078311 a078311 = a020639 . a078310 -- _Reinhard Zumkeller_, Jul 23 2013 %o A078311 (PARI) a(n) = factor(1 + n * vecprod(factor(n)[, 1]))[1,1]; \\ _Amiram Eldar_, Apr 10 2025 %Y A078311 Cf. A007947, A020639, A078310, A078312. %K A078311 nonn,easy %O A078311 1,1 %A A078311 _Reinhard Zumkeller_, Nov 23 2002