A074846 - OEIS

%I #15 Jan 30 2025 21:03:05

%S 2,3,4,7,6,7,10,9,12,13,18,13,24,15,16,21,18,21,22,21,22,28,26,25,28,

%T 33,28,34,32,33,36,36,34,37,42,43,40,39,48,43,42,46,46,47,48,51,50,54,

%U 52,51,56,55,56,55,58,60,58,61,60,67,66,63,66,67,68,67,70,75,70,79,72,79

%N a(n) is the smallest k > n such that n*k+1 is prime.

%e a(1)=2 because 1*2+1=3 is the smallest prime of the form 1*k+1 with k > 1.

%e a(4)=7 because 4*7+1=29 is the smallest prime of the form 4*k+1 with k > 4.

%e a(100)=103 because 100*103+1=10301 is the smallest prime of the form 100*k+1 with k > 100.

%K nonn

%O 1,1

%A _Zak Seidov_, Sep 10 2002

%E a(20) corrected by _Sean A. Irvine_, Jan 30 2025