A087461 Arithmetic mean of n-th and 2n-th primes.

5, 9, 13, 20, 25, 30, 36, 42, 50, 55, 63, 71, 75, 80, 92, 99, 106, 115, 122, 127, 136, 141, 156, 163, 170, 177, 185, 190, 197, 210, 221, 227, 238, 249, 255, 265, 273, 282, 291, 300, 307, 317, 325, 330, 339, 351, 363, 374, 385, 395, 404, 409, 422, 429, 438, 444

Offset: 2

Author

Gary W. Adamson, Sep 07 2003

Keywords

• nonn
• easy

Comments

A rather sparse subset are primes: 5, 13, 71, = a(2), a(4), a(13).

Examples

			Series begins with 2nd prime, 3 and 4th prime, 7. Then (3 + 7)/2 = 5.
		

Links

• Seiichi Manyama, Table of n, a(n) for n = 2..10000

Crossrefs

Cf. A000040, A092390, A258934.

Programs

Mathematica

Table[Mean[{Prime[n],Prime[2n]}],{n,2,60}] (* Harvey P. Dale, May 25 2011 *)

Formula

a(n) = (n-th prime + 2n-th prime)/2

Extensions

More terms from Ray Chandler and Rick L. Shepherd, Sep 09 2003