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A108809 Numbers n such that both n+(n-1)^2 and n+(n+1)^2 are primes.

%I A108809 #9 Feb 09 2017 06:11:58
%S A108809 2,3,4,7,9,15,18,25,34,55,58,63,67,100,102,139,144,148,154,162,163,
%T A108809 168,190,195,219,232,247,267,280,289,330,349,379,384,417,427,448,454,
%U A108809 477,568,580,643,645,669,672,727,762,793,802,813,837,847,900,975,988,993
%N A108809 Numbers n such that both n+(n-1)^2 and n+(n+1)^2 are primes.
%H A108809 Ivan Neretin, <a href="/A108809/b108809.txt">Table of n, a(n) for n = 1..10000</a>
%e A108809 34 is in the sequence because 34 + 33^2 = 1123 and 34 + 35^2 = 1259 are both prime.
%p A108809 L:=[]; for k from 1 to 1000 do if isprime(k+(k-1)^2) and isprime(k+(k+1)^2) then L:=[op(L),k] fi od;
%t A108809 Select[Range@1000, PrimeQ[#^2 - # + 1] && PrimeQ[#^2 + 3 # + 1] &] (* _Ivan Neretin_, Feb 08 2017 *)
%o A108809 (PARI) isok(n) = isprime(n+(n-1)^2) && isprime(n+(n+1)^2); \\ _Michel Marcus_, Feb 08 2017
%Y A108809 Cf. A027861.
%Y A108809 Intersection of A055494 and A094210. - _Michel Marcus_, Feb 08 2017
%K A108809 easy,nonn
%O A108809 1,1
%A A108809 _Walter Kehowski_, Jul 04 2005