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 A156592 Product p*q of two primes with q = 2*p + 1. 12

%I

%S 10,21,55,253,1081,1711,3403,5671,13861,15931,25651,34453,60031,64261,

%T 73153,108811,114481,126253,158203,171991,258121,351541,371953,392941,

%U 482653,518671,703891,822403,853471,869221,933661,1034641,1104841

%N Product p*q of two primes with q = 2*p + 1.

%C Subsequence of A068443.

%C Products of Sophie Germain primes p with their corresponding safe primes 2p+1. The smallest prime factor of a(n) is (a(n) - phi(a(n)))/3 and the largest prime factor of a(n) is 2(a(n) - phi(a(n)))/3 + 1. - _Wesley Ivan Hurt_, Oct 03 2013

%H Vincenzo Librandi, <a href="/A156592/b156592.txt">Table of n, a(n) for n = 1..4000</a>

%H <a href="http://dxdy.ru/topic16349.html">Math Marathon (MM95)</a> (in Russian) [from Vladimir Joseph Stephan Orlovsky, May 12 2010]

%F a(n) = A005384(n)*A005385(n).

%t lst={};Do[p=Prime[n];q=2*p+1;If[PrimeQ[q],AppendTo[lst,p*q]],{n,5!}];lst (* _Vladimir Joseph Stephan Orlovsky_, May 12 2010 *)

%Y Cf. A005384, A005385. Subset of A001358.

%K nonn

%O 1,1

%A _Reinhard Zumkeller_, Feb 10 2009

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Last modified May 18 18:33 EDT 2021. Contains 343998 sequences. (Running on oeis4.)