A087461 - OEIS

%I #16 Jan 17 2020 10:38:52

%S 5,9,13,20,25,30,36,42,50,55,63,71,75,80,92,99,106,115,122,127,136,

%T 141,156,163,170,177,185,190,197,210,221,227,238,249,255,265,273,282,

%U 291,300,307,317,325,330,339,351,363,374,385,395,404,409,422,429,438,444

%N Arithmetic mean of n-th and 2n-th primes.

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

%H Seiichi Manyama, <a href="/A087461/b087461.txt">Table of n, a(n) for n = 2..10000</a>

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

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

%t Table[Mean[{Prime[n],Prime[2n]}],{n,2,60}] (* _Harvey P. Dale_, May 25 2011 *)

%Y Cf. A000040, A092390, A258934.

%K nonn,easy

%O 2,1

%A _Gary W. Adamson_, Sep 07 2003

%E More terms from _Ray Chandler_ and _Rick L. Shepherd_, Sep 09 2003