1,2

It is conjectured that nonzero terms exist for each n: see A089727, the main entry.

a(n) = n iff n is a term of A005574.

Table of n, a(n) for n=1..73.

(PARI) {A171751(n) = local(k); k=n; while(!isprime(n*k+1) && k>0, k--); k}

Cf. A089727 (corresponding primes), A005574.

Sequence in context: A054929 A236628 A078429 * A124676 A076249 A062170

Adjacent sequences: A171748 A171749 A171750 * A171752 A171753 A171754

nonn

Rick L. Shepherd, Dec 17 2009

approved