A128234 Values of n such that the average of p(n) and p(p(n)), where p(k) denotes the k-th prime, is prime.

8, 9, 11, 12, 19, 23, 28, 62, 64, 68, 71, 85, 95, 104, 114, 115, 131, 134, 175, 178, 181, 182, 200, 216, 240, 246, 247, 250, 266, 276, 277, 316, 346, 372, 382, 421, 429, 438, 440, 444, 445, 458, 469, 485, 494, 511, 518, 541, 543, 566, 568, 594, 596, 601, 604

Offset

2,1

Links

Table of n, a(n) for n=2..56.

Example

9 is in the sequence because p(9)=23, p(23)=83 and (23+83)/2 is prime.

Maple

a:=proc(n) if isprime((ithprime(n)+ithprime(ithprime(n)))/2)=true then n else fi end: seq(a(n), n=2..800);

Mathematica

Select[Range[700], PrimeQ[Mean[{Prime[#], Prime[Prime[#]]}]]&] (* Harvey P. Dale, Nov 18 2020 *)

Crossrefs

Cf. A128233.

Sequence in context: A114460 A120201 A188056 * A368082 A308602 A087668

Adjacent sequences: A128231 A128232 A128233 * A128235 A128236 A128237

Keyword

nonn

Author

Emeric Deutsch, Feb 20 2007

Status

approved