The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A128234 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
Showing all changes.

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.
(history; published version)

#4 by Harvey P. Dale at Wed Nov 18 17:55:34 EST 2020

STATUS

editing

approved

#3 by Harvey P. Dale at Wed Nov 18 17:55:32 EST 2020

MATHEMATICA

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

STATUS

approved

editing

#2 by Russ Cox at Fri Mar 30 17:36:13 EDT 2012

AUTHOR

_Emeric Deutsch (deutsch(AT)duke.poly.edu), _, Feb 20 2007

Discussion

Fri Mar 30

17:36

OEIS Server: https://oeis.org/edit/global/173

#1 by N. J. A. Sloane at Fri May 11 03:00:00 EDT 2007

NAME

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

DATA

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

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);

CROSSREFS

Cf. A128233.

KEYWORD

nonn

AUTHOR

Emeric Deutsch (deutsch(AT)duke.poly.edu), Feb 20 2007

STATUS

approved