cp's OEIS Frontend

A196670 The Chebyshev primes of index 4.

%I A196670 #30 Sep 08 2022 08:45:59
%S A196670 5,7,17,19,31,37,41,43,53,59,67,73,79,83,101,103,107,127,131,149,157,
%T A196670 163,179,181,197,199,211,223,227,257,269,277,281,317,331,337,347,353,
%U A196670 379,389,419,421,439,461,463,467,479,491,499,509,541,563,569,577,617
%N A196670 The Chebyshev primes of index 4.
%C A196670 The sequence consists of such odd prime numbers p that satisfy li(psi(p^4)) - li(psi(p^4-1)) < 1/4, where li(x) is the logarithmic integral and psi(x) is the Chebyshev psi function.
%H A196670 Dana Jacobsen, <a href="/A196670/b196670.txt">Table of n, a(n) for n = 1..75</a>
%H A196670 M. Planat and P. Solé, <a href="http://arxiv.org/abs/1109.6489">Efficient prime counting and the Chebyshev primes</a> arXiv:1109.6489 [math.NT], 2011.
%p A196670 # The function PlanatSole(n,r) is in A196667.
%p A196670 A196670 := n -> PlanatSole(n,4); # _Peter Luschny_, Oct 23 2011
%t A196670 ChebyshevPsi[n_] := Log[LCM @@ Range[n]];
%t A196670 Reap[Do[If[LogIntegral[ChebyshevPsi[p^4]] - LogIntegral[ChebyshevPsi[p^4 - 1]] < 1/4, Print[p]; Sow[p]], {p, Prime[Range[2, 120]]}]][[2, 1]] (* _Jean-François Alcover_, Jul 14 2018, updated Dec 06 2018 *)
%o A196670 (Magma)
%o A196670 Mangoldt:=function(n);
%o A196670 if #Factorization(n) eq 1 then return Log(Factorization(n)[1][1]); else return 0; end if;
%o A196670 end function;
%o A196670 tcheb:=function(n);
%o A196670 x:=0;
%o A196670 for i in [1..n] do
%o A196670 x:=x+Mangoldt(i);
%o A196670 end for;
%o A196670 return(x);
%o A196670 end function;
%o A196670 jump4:=function(n);
%o A196670 x:=LogIntegral(tcheb(NthPrime(n)^4))-LogIntegral(tcheb(NthPrime(n)^4-1));
%o A196670 return x;
%o A196670 end function;
%o A196670 Set4:=[];
%o A196670 for i in [2..1000] do
%o A196670 if jump4(i)-1/4 lt 0 then Set4:=Append(Set4,NthPrime(i)); NthPrime(i); end if;
%o A196670 end for;
%o A196670 Set4;
%o A196670 (Sage)
%o A196670 def A196670(n) : return PlanatSole(n,4)
%o A196670 # The function PlanatSole(n,r) is in A196667.
%o A196670 # _Peter Luschny_, Oct 23 2011
%o A196670 (Perl) use ntheory ":all"; forprimes { say if 4 *(LogarithmicIntegral(chebyshev_psi($_**4)) - LogarithmicIntegral(chebyshev_psi($_**4-1))) < 1 } 3,100; # _Dana Jacobsen_, Dec 29 2015
%Y A196670 Cf. A196667, A196668, A196669.
%K A196670 nonn
%O A196670 1,1
%A A196670 _Michel Planat_, Oct 05 2011
%E A196670 More terms from _Dana Jacobsen_, Dec 29 2015