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Prime numbers p such that pi(p) + 2*p is a square.
3

%I #11 Jun 01 2021 11:45:24

%S 43,113,331,1019,1559,1613,2087,2551,3217,5471,6317,7109,7583,7703,

%T 11777,13967,15649,18353,21277,22921,24847,27767,27997,29167,66617,

%U 86531,91081,91921,112289,116041,122267,122753,123727,125197,138289

%N Prime numbers p such that pi(p) + 2*p is a square.

%F a(n) = prime(A104776(n)).

%t Select[Prime[Range[13000]],IntegerQ[Sqrt[PrimePi[#]+2 #]]&] (* _Harvey P. Dale_, Jun 01 2021 *)

%o (PARI) lista(nn) = {vec = vector(nn, i, prime(i)); pp = select(i->(issquare(2*i+primepi(i))), vec); pp;} \\ _Michel Marcus_, Oct 09 2013

%Y Cf. A104776.

%K nonn

%O 1,1

%A _Zak Seidov_, Apr 23 2005