A114228 Smallest number m such that prime(n)+2*prime(m) is a prime.

1, 2, 1, 2, 1, 2, 1, 2, 4, 2, 1, 2, 1, 2, 2, 4, 2, 1, 6, 2, 1, 2, 4, 1, 2, 1, 2, 1, 4, 1, 2, 4, 3, 4, 2, 2, 1, 2, 2, 4, 3, 2, 1, 4, 7, 5, 1, 2, 1, 2, 8, 3, 2, 2, 2, 4, 2, 1, 6, 3, 4, 1, 2, 1, 4, 2, 3, 2, 1, 2, 4, 2, 2, 1, 2, 12, 1, 8, 3, 4, 3, 6, 2, 1, 2, 4, 1, 2, 1, 12, 11, 1, 14, 1, 2, 4, 6, 7, 2, 3, 2, 2, 8

Offset: 2

Author

Lei Zhou, Nov 18 2005

Keywords

• easy
• nonn

Comments

a(A114229(n)) = n for n >=1 and a(m) <> n for m < A114229(n). - Reinhard Zumkeller, Oct 31 2013

Examples

			prime(2)=3, 3+2*prime(1)=7 is prime, so a(2)=1;
prime(3)=5, 5+2*prime(2)=11 is prime, so a(3)=2;
...
prime(20)=71, 71+2*prime(6)=97 is prime, so a(20)=6.
		

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 2..10000

Crossrefs

Cf. A114227.

Cf. A010051, A000040.

Programs

Haskell

a114228 n = head [m | m <- [1..],
                      a010051 (a000040 n + 2 * a000040 m) == 1]
-- Reinhard Zumkeller, Oct 31 2013

Mathematica

Table[p1 = Prime[n1]; n2 = 1; p2 = 2; While[ cp = p1 + 2*p2; ! PrimeQ[cp], n2++; p2 = Prime[n2]]; n2, {n1, 2, 201}]