A087030 n "reflected" in the next prime: a(n)=2p-n, p is smallest prime > n.

3, 4, 7, 6, 9, 8, 15, 14, 13, 12, 15, 14, 21, 20, 19, 18, 21, 20, 27, 26, 25, 24, 35, 34, 33, 32, 31, 30, 33, 32, 43, 42, 41, 40, 39, 38, 45, 44, 43, 42, 45, 44, 51, 50, 49, 48, 59, 58, 57, 56, 55, 54, 65, 64, 63, 62, 61, 60, 63, 62, 73, 72, 71, 70, 69, 68, 75, 74, 73, 72, 75

Offset: 1

Author

Zak Seidov, Jul 31 2003

Keywords

• easy
• nonn

Comments

Take any n, find the distance from n to p: d=p-n, where p is the smallest prime > n ("next prime"), then a(n) is the number which is at the same distance from p as n, a(n)=p+d. n such that p+d=2p-n is prime in A087031.

Examples

			a(2)=4 because smallest prime >2 is 3 and 2*3-2=4.
		

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A087031.

Programs

Mathematica

Table[2NextPrime[n]-n,{n,80}] (* Harvey P. Dale, Jun 29 2011 *)

PARI

a(n)=2*nextprime(n+1)-n \\ Charles R Greathouse IV, Oct 03 2013

Formula

a(n)=2p-n, p is the smallest prime > n.