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 A087711 a(n) = smallest number k such that both k-n and k+n are primes. 5

%I

%S 2,4,5,8,7,8,11,10,11,14,13,18,17,16,17,22,21,20,23,22,23,26,25,30,29,

%T 28,33,32,31,32,37,36,35,38,37,38,43,42,41,44,43,48,47,46,57,52,51,50,

%U 53,52,53,56,55,56,59,58,75,70,69,72,67,66,65,68,67,72,71,70,71,80,81,78

%N a(n) = smallest number k such that both k-n and k+n are primes.

%H Zak Seidov, <a href="/A087711/b087711.txt">Table of n, a(n) for n=0..1000.</a>

%e n=10: k=13 because 13-10 and 13+10 are both prime and 13 is the smallest k such that k +/- 10 are both prime

%e 4-1=3, prime, 4+1=5, prime; 5-2=3, 5+2=7; 8-3=5, 8+3=11; 9-4=5, 9+4=13, ...

%t s = ""; k = 0; For[i = 3, i < 22^2, If[PrimeQ[i - k] && PrimeQ[i + k], s = s <> ToString[i] <> ","; k++ ]; i++ ]; Print[s] - _Vladimir Joseph Stephan Orlovsky_, Apr 03 2008

%o (MAGMA) distance:=function(n); k:=n+2; while not IsPrime(k-n) or not IsPrime(k+n) do k:=k+1; end while; return k; end function; [ distance(n): n in [1..71] ]; /* Klaus Brockhaus, Apr 08 2007 */

%Y Cf. A087695, A087696, A087697, A087678, A087679, A087680, A087681, A087682, A087683.

%Y Cf. A082467. See A137169 for another version.

%K easy,nonn

%O 0,1

%A _Zak Seidov_, Sep 28 2003

%E Entries checked by _Klaus Brockhaus_, Apr 08 2007

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