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%I #22 Nov 02 2024 04:07:52
%S 1,2,5,7,10,11,16,20,22,25,37,40,41,46,50,55,61,62,65,77,85,91,92,101,
%T 106,107,116,122,125,127,130,131,142,145,146,152,155,161,172,181,182,
%U 187,196,197,206,220,221,232,235,241,242,257,260,262,265,271,275,280,281,286,295,310,317,325,326,346,356,362,380,382,386,391
%N Numbers m such that m^2 + (m+3)^2 is prime.
%H Zak Seidov, <a href="/A224870/b224870.txt">Table of n, a(n) for n = 1..1000</a>
%F a(n) = (1/2)*(sqrt(2*A076727(n) - k^2) - k), k = 3.
%p A224870:=n->`if`(isprime(n^2 + (n+3)^2), n, NULL): seq(A224870(n), n=1..10^3); # _Wesley Ivan Hurt_, Feb 11 2017
%t k = 3; Select[Range[500], PrimeQ[#^2 + (# + k)^2]&]
%o (PARI) isok(n) = isprime(n^2 + (n+3)^2); \\ _Michel Marcus_, Feb 13 2017
%Y Cf. A027861, A027862, A076727.
%K nonn
%O 1,2
%A _Zak Seidov_, Jul 22 2013