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 A224872 Numbers k such that prime(k)*pi(k)+1 is prime. 1
 3, 15, 20, 29, 58, 63, 80, 90, 92, 93, 96, 116, 125, 126, 143, 151, 155, 156, 164, 182, 185, 189, 210, 230, 251, 255, 256, 268, 274, 275, 294, 298, 319, 323, 324, 325, 328, 330, 343, 360, 362, 399, 400, 416, 425, 429, 437, 446, 457, 463, 466, 480, 497, 505, 506 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Charles R Greathouse IV, Table of n, a(n) for n = 1..10000 EXAMPLE Prime(126)*pi(126)+1 = 701*30+1 = 21031 which is prime, hence 126 is in the sequence. MAPLE A224872:=proc(n) local a; a:=(ithprime(n)*numtheory[pi](n)+1) ; if isprime(a) then RETURN(n) end if:end proc: seq(A224872(n), n=1..600); MATHEMATICA Select[Range[2000], PrimeQ[Prime[#]*PrimePi[#]+1]&] PROG (PARI) n=0; forprime(p=2, 1e5, if(isprime(p*primepi(n++)+1), print1(n", "))) \\ Charles R Greathouse IV, Jul 23 2013 CROSSREFS Cf. A065042. Sequence in context: A124877 A111517 A083545 * A097571 A048087 A316751 Adjacent sequences: A224869 A224870 A224871 * A224873 A224874 A224875 KEYWORD nonn AUTHOR K. D. Bajpai, Jul 23 2013 STATUS approved

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Last modified August 7 20:39 EDT 2024. Contains 375017 sequences. (Running on oeis4.)