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%I #9 Nov 27 2017 00:21:02
%S 4,5,10,9,26,13,78,17,64,21,56,61,40,239,46,81,290,55,58,41,148,45,
%T 162,73,76,131,136,57,320,61,528,65,100,69,666,253,186,77,118,681,206,
%U 85,130,89,136,231,236,97,148,101,562,885,372,163,606,113,628,175,650,181
%N Least k such that (k-1)/n and k*n + 1 both are primes.
%C Obviously a(n) is odd or even as n is even or odd.
%H Harvey P. Dale, <a href="/A092961/b092961.txt">Table of n, a(n) for n = 1..1000</a>
%e a(4) = 9 as (9-1)/4 = 2 and 9*4 + 1 = 37 both are primes.
%e a(9) = 64, (64-1)/9 = 7 and 64*9 + 1 = 577 both are primes.
%t bp[n_]:=Module[{k=2n+1},While[!PrimeQ[(k-1)/n]||!PrimeQ[k*n+1],k++];k]; Array[bp,60] (* _Harvey P. Dale_, Feb 23 2014 *)
%o (PARI) a(n)=for(i=1,10+n^3,if(Mod(i-1,n)==0 && isprime((i-1)/n) && isprime(i*n+1),return(i)))
%Y Cf. A092962, A092963.
%K nonn
%O 1,1
%A _Amarnath Murthy_, Mar 25 2004
%E More terms from Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 26 2004
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