%I #10 Jul 13 2013 12:02:28

%S 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 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 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 Smallest k such that nk-1 is prime.

%H Reinhard Zumkeller, <a href="/A053989/b053989.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = (A038700(n)+1)/n.

%e a(5)=4 because the smallest prime in the sequence 5k-1 (4,9,14,19,24...) is 19 when k=4

%o (Haskell)

%o a053989 n = head [k | k <- [1..], a010051' (k * n - 1) == 1]

%o -- _Reinhard Zumkeller_, Feb 14 2013

%o (PARI) a(n)=my(j);while(!isprime(j++*n-1),);j \\ _Charles R Greathouse IV_, Apr 18 2013

%Y Cf. A034693, A038700, A071558, A010051, A103689, A200996.

%K easy,nonn

%O 1,1

%A _Henry Bottomley_, Apr 04 2000