A136027 Smallest prime of the form (p-2n)/(2n+1) with p prime.

3, 3, 5, 5, 3, 7, 3, 3, 5, 3, 5, 5, 3, 5, 13, 3, 3, 11, 5, 3, 5, 3, 5, 5, 19, 3, 7, 3, 5, 7, 3, 5, 5, 11, 3, 13, 5, 3, 7, 7, 3, 5, 3, 17, 7, 5, 3, 11, 5, 23, 5, 3, 5, 5, 3, 5, 7, 3, 11, 7, 3, 3, 5, 5, 3, 5, 5, 3, 11, 3, 3, 13, 3, 11, 11, 7, 3, 5, 5, 3, 5, 3, 11, 5, 3, 3, 5, 5

Offset: 1

Author

Artur Jasinski, Dec 10 2007

Keywords

• nonn
• easy

Comments

The associated p are in A136026.

Examples

			a(1)=3 because 3 is smallest prime of the form (p-2)/3; in this case prime(k)=11.
a(2)=3 because 3 is smallest prime of the form (p-4)/5; in this case prime(k)=19.
a(3)=5 because 5 is smallest prime of the form (p-6)/7; in this case prime(k)=41.
		

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A136019, A136020, A136026.

Programs

Mathematica

a = {}; Do[k = 1; While[ !PrimeQ[(Prime[k] - 2n)/(2n + 1)], k++ ]; AppendTo[a, (Prime[k] - 2n)/(2n + 1)], {n, 1, 100}]; a

PARI

a(n)=forprime(p=2,,if(isprime(2*n*(p+1)+p),return(p))) \\ Charles R Greathouse IV, Mar 21 2013

Extensions

Edited by R. J. Mathar, May 17 2009