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

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, 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, 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

Offset: 1

Author

Benoit Cloitre, Apr 27 2003

Keywords

• nonn

Links

• R. J. Mathar, Table of n, a(n) for n = 1..1000

Programs

Maple

A082466 := proc(n)
    local k,p ;
    for k from 1 do
        p := (n+k)*n-1 ;
        if isprime(p) and isprime(p+2) then
            return k;
        end if;
    end do:
end proc: # R. J. Mathar, Jul 20 2012

Mathematica

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 *)

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)