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%I #18 Nov 06 2017 02:48:12
%S 3,5,13,17,29,31,43,67,71,97,107,109,131,157,181,191,223,233,239,269,
%T 281,313,359,379,383,401,409,431,503,523,569,571,619,631,659,691,719,
%U 751,787,797,857,859,881,883,971,1039,1061,1063,1091,1117,1123,1201
%N Primes which occur exactly twice in the sequence of a(n) = prime(n) - prime(n - pi(n)) = A065308(n).
%C In A065308, each odd prime seems to appear once or twice.
%H Harry J. Smith, <a href="/A065311/b065311.txt">Table of n, a(n) for n = 1..1000</a>
%t Most@ Select[Tally@ Array[Prime[# - PrimePi@ #] &, 300], Last@ # == 2 &][[All, 1]] (* _Michael De Vlieger_, Nov 03 2017 *)
%o (PARI) { n=0; p=1; f=2; m=1; for (i=1, 10^9, a=0; p=nextprime(p + 1); while (p==f, a++; m++; f=prime(m - primepi(m))); if (a==2, write("b065311.txt", n++, " ", p); if (n==1000, return)) ) } \\ _Harry J. Smith_, Oct 16 2009
%Y Cf. A000040, A000720, A054546, A065308, A065309, A065310, A065311.
%K nonn
%O 1,1
%A _Labos Elemer_, Oct 29 2001
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