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 A053989 #10 Jul 13 2013 12:02:28 %S A053989 3,2,1,1,4,1,2,1,2,2,4,1,8,1,2,2,4,1,2,1,2,2,6,1,6,4,2,3,6,1,2,1,4,2, %T A053989 4,2,2,1,6,2,4,1,6,1,2,3,6,1,2,3,2,2,4,1,2,3,2,3,6,1,8,1,4,2,6,2,6,1, %U A053989 2,2,4,1,14,1,2,2,4,3,2,1,8,2,4,1,6,3,2,3,16,1,2,4,6,3,4,2,2,1,2,2 %N A053989 Smallest k such that nk-1 is prime. %H A053989 Reinhard Zumkeller, <a href="/A053989/b053989.txt">Table of n, a(n) for n = 1..10000</a> %F A053989 a(n) = (A038700(n)+1)/n. %e A053989 a(5)=4 because the smallest prime in the sequence 5k-1 (4,9,14,19,24...) is 19 when k=4 %o A053989 (Haskell) %o A053989 a053989 n = head [k | k <- [1..], a010051' (k * n - 1) == 1] %o A053989 -- _Reinhard Zumkeller_, Feb 14 2013 %o A053989 (PARI) a(n)=my(j);while(!isprime(j++*n-1),);j \\ _Charles R Greathouse IV_, Apr 18 2013 %Y A053989 Cf. A034693, A038700, A071558, A010051, A103689, A200996. %K A053989 easy,nonn %O A053989 1,1 %A A053989 _Henry Bottomley_, Apr 04 2000