A103959 Minimum prime p such that prime(n)*p - 2 is prime.

2, 3, 3, 3, 3, 3, 5, 7, 3, 11, 13, 3, 11, 3, 3, 3, 5, 3, 3, 3, 7, 19, 11, 5, 7, 5, 3, 23, 7, 3, 3, 5, 3, 7, 5, 31, 7, 3, 3, 5, 17, 3, 3, 3, 5, 19, 3, 7, 29, 7, 5, 5, 61, 3, 3, 3, 11, 3, 3, 11, 7, 3, 3, 5, 3, 5, 3, 3, 3, 7, 11, 11, 19, 3, 61, 5, 29, 7, 3, 7, 17

Offset: 1

Author

Lei Zhou, Feb 22 2005

Keywords

• easy
• nonn

Comments

Conjecture: a(n) <= prime(n). Tested to n=10000.

Examples

			Prime(1)*2-2=2 is prime, so a(1)=2;
Prime(2)*3-2=7 is prime, so a(2)=3;
		

Links

• T. D. Noe, Table of n, a(n) for n = 1..10000

Programs

Mathematica

Table[p=Prime[n]; k=1; pk=Prime[k]; cp=p*pk-2; While[ !PrimeQ[cp], k=k+1; pk=Prime[k]; cp=p*pk-2]; pk, {n, 100}]