cp's OEIS Frontend

A174798 Numbers n such that 2*prime(n) and 2*prime(n+1) are consecutive semiprimes.

%I A174798 #7 Nov 21 2013 12:50:01
%S A174798 1,3,10,33,43,49,50,57,63,100,113,120,131,140,149,159,173,195,206,224,
%T A174798 230,277,284,303,315,320,332,366,373,394,395,401,448,463,469,471,473,
%U A174798 477,483,484,492,513,524,530,534,537,543,555,558,576,577,592,600,608
%N A174798 Numbers n such that 2*prime(n) and 2*prime(n+1) are consecutive semiprimes.
%C A174798 There are no semiprimes strictly between 2*prime(n) and 2*prime(n+1).
%C A174798 A174956(A100484(a(n+1)))=A174956(A100484(a(n)))+1. [From _Reinhard Zumkeller_, Apr 03 2010]
%F A174798 A000040(a(n)) = A001358(A174797(n))/2.
%e A174798 a(1)=1 because 2*prime(1)=4=semiprime(1) and 2*prime(1+1)=6=semiprime(2).
%e A174798 a(2)=3 because 2*prime(3)=10=semiprime(4) and 2*prime(3+1)=14=semiprime(5).
%t A174798 PrimePi[First[#]]&/@Select[Partition[Select[Range[20000],PrimeOmega[#] == 2&], 2,1]/2,And@@IntegerQ/@#&] (* _Harvey P. Dale_, Nov 19 2011 *)
%Y A174798 Cf. A000040, A001358, A174797.
%K A174798 nonn
%O A174798 1,2
%A A174798 _Juri-Stepan Gerasimov_, Mar 29 2010
%E A174798 Edited, corrected and extended by _Ray Chandler_, Apr 07 2010