A088631 Largest number m < n such that m+n is a prime.

1, 2, 3, 2, 5, 6, 5, 8, 9, 8, 11, 10, 9, 14, 15, 14, 13, 18, 17, 20, 21, 20, 23, 22, 21, 26, 25, 24, 29, 30, 29, 28, 33, 32, 35, 36, 35, 34, 39, 38, 41, 40, 39, 44, 43, 42, 41, 48, 47, 50, 51, 50, 53, 54, 53, 56, 55, 54, 53, 52, 51, 50, 63, 62, 65, 64, 63, 68, 69, 68, 67, 66, 65, 74, 75

Offset: 2

Author

N. J. A. Sloane, Nov 24 2003

Keywords

• easy
• nonn

Examples

			Adding 1,2,3,2,5 to 2,3,4,5,6 we get the primes 3,5,7,7,11.
		

Links

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

Crossrefs

Cf. A088633. Second column of A088643.

Cf. A010051, A060265, A007917.

Programs

Haskell

a088631 n = a060265 n - n  -- Reinhard Zumkeller, Feb 22 2015

Maple

with(numtheory); A088631 := n->prevprime(2*n)-n;

Formula

a(n) = p-n where p = largest prime <= 2n-1.

a(n) = A060265(n) - n. - Reinhard Zumkeller, Feb 22 2015