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A093701 a(n) = smallest m>a(n-1) such that 1+m*n is prime, a(1) = 1. 2

%I

%S 1,2,4,7,8,10,16,17,18,19,30,31,34,35,36,37,38,41,58,59,62,64,72,73,

%T 76,77,80,81,84,85,88,95,96,97,102,103,106,111,114,118,122,123,124,

%U 125,130,132,134,135,138,140,142,144,150,152,156,158,164,166,174,175

%N a(n) = smallest m>a(n-1) such that 1+m*n is prime, a(1) = 1.

%C A093702(n) = 1+a(n)*n.

%H Harvey P. Dale, <a href="/A093701/b093701.txt">Table of n, a(n) for n = 1..1000</a>

%e For n=3: we have a(2)=2, so we want the smallest number m > 2 such that n*m+1 = 3*m+1 is prime. m=3 fails but m=4 works, so a(3) = m = 4. - _N. J. A. Sloane_, Dec 13 2018

%t nxt[{n_,a_}]:=Module[{m=a+1},While[!PrimeQ[m(n+1)+1],m++];{n+1,m}]; NestList[ nxt,{1,1},60][[All,2]] (* _Harvey P. Dale_, Dec 13 2018 *)

%Y Cf. A013632, A093702.

%Y Note that A081942 is a related but distinct sequence.

%K nonn

%O 1,2

%A _Reinhard Zumkeller_, Apr 10 2004

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Last modified June 13 15:33 EDT 2021. Contains 345008 sequences. (Running on oeis4.)