OFFSET
2,1
COMMENTS
A rather sparse subset are primes: 5, 13, 71, = a(2), a(4), a(13).
LINKS
Seiichi Manyama, Table of n, a(n) for n = 2..10000
FORMULA
a(n) = (n-th prime + 2n-th prime)/2
EXAMPLE
Series begins with 2nd prime, 3 and 4th prime, 7. Then (3 + 7)/2 = 5.
MATHEMATICA
Table[Mean[{Prime[n], Prime[2n]}], {n, 2, 60}] (* Harvey P. Dale, May 25 2011 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Gary W. Adamson, Sep 07 2003
EXTENSIONS
More terms from Ray Chandler and Rick L. Shepherd, Sep 09 2003
STATUS
approved