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 A063713 Numbers n such that there exist primes p, q, r with n*2 = p - r = r + q (values of r are given in A063714. 3

%I

%S 4,5,6,7,8,9,10,11,12,13,15,16,17,18,20,21,22,23,24,25,27,28,30,32,33,

%T 35,36,38,39,42,43,45,46,48,50,51,52,53,54,55,57,58,60,63,65,66,67,69,

%U 70,71,72,75,77,78,80,81,84,85,87,88,90,93,96,97,98,99,100,101,102,105

%N Numbers n such that there exist primes p, q, r with n*2 = p - r = r + q (values of r are given in A063714.

%H Robert Israel, <a href="/A063713/b063713.txt">Table of n, a(n) for n = 1..10000</a>

%e 10*2 = 20 = 23 - 3 = 3 + 17, A063714(7) = 3; 11*2 = 22 = 41 - 19 = 19 + 3, A063714(8) = 19 28 is missing because we have the prime sums (Goldbach): 5 + 23 = 11 + 17 and differences with primes less 28: 31 - 3 = 41 - 13 = 47 - 19; none of these have a prime in common.

%p filter:= proc(n) local k;

%p k:= 1;

%p while k < 2*n do

%p k:= nextprime(k);

%p if isprime(2*n+k) and isprime(2*n-k) then return true fi

%p od;

%p false

%p end proc:

%p select(filter, [\$1..1000]); # _Robert Israel_, Oct 09 2017

%t okQ[n_] := AnyTrue[Prime[Range[PrimePi[2 n - 2]]], PrimeQ[2 n + #] && PrimeQ[2 n - #]&]; Select[Range, okQ] (* _Jean-François Alcover_, Feb 12 2018 *)

%Y Cf. A063714, A002373, A020483.

%K nonn

%O 1,1

%A _Reinhard Zumkeller_, Aug 10 2001

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Last modified June 17 13:59 EDT 2021. Contains 345083 sequences. (Running on oeis4.)