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 A082466 Least k>=1 such that n^2+kn-1 and n^2+kn+1 are twin primes. 3

%I

%S 3,1,1,11,1,1,53,1,3,5,7,3,11,16,1,11,43,6,11,1,1,8,13,1,17,7,3,11,43,

%T 4,11,4,7,8,31,9,17,1,9,35,1,4,53,4,7,41,43,6,23,1,17,8,67,1,5,4,17,

%U 11,1,7,197,4,3,11,25,1,227,7,3,14,157,19,11,16,3,71,43,6,53,7,7,44,31,3,41

%N Least k>=1 such that n^2+kn-1 and n^2+kn+1 are twin primes.

%H R. J. Mathar, <a href="/A082466/b082466.txt">Table of n, a(n) for n = 1..1000</a>

%p A082466 := proc(n)

%p local k,p ;

%p for k from 1 do

%p p := (n+k)*n-1 ;

%p if isprime(p) and isprime(p+2) then

%p return k;

%p end if;

%p end do:

%p end proc: # _R. J. Mathar_, Jul 20 2012

%t lk[n_]:=Module[{k=1},While[!And@@PrimeQ[n^2+k*n+{1,-1}],k++];k]; Array[ lk,90] (* _Harvey P. Dale_, Nov 25 2013 *)

%o (PARI) a(n)=if(n<0,0,k=1; while(isprime(n^2+k*n+1)*isprime(n^2+k*n-1)==0,s++); k)

%K nonn

%O 1,1

%A _Benoit Cloitre_, Apr 27 2003

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Last modified July 21 19:13 EDT 2019. Contains 325199 sequences. (Running on oeis4.)