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A177215 Numbers k that are the products of two distinct primes such that 2*k-1, 4*k-3, 8*k-7, 16*k-15, 32*k-31 and 64*k-63 are also products of two distinct primes. 6

%I

%S 694,3403,4714,5062,5353,7495,11293,12139,13798,14191,19735,21439,

%T 22585,24277,25009,25399,26734,26899,31261,32959,35299,36199,44869,

%U 48949,49471,50797,58003,60181,62521,70759,72397,73909,75631,79021,83086

%N Numbers k that are the products of two distinct primes such that 2*k-1, 4*k-3, 8*k-7, 16*k-15, 32*k-31 and 64*k-63 are also products of two distinct primes.

%e 694 is a term because 694 = 2*347, 2*694 - 1 = 1387 = 19*73, 4*694 - 1 = 2773 = 47*59, 8*694 - 1 = 5545 = 5*1109, 16*694 - 1 = 11089 = 13*853, 32*694 - 1 = 22177 = 67*331, and 64*694 - 1 = 44353 = 17*3609.

%t f[n_]:=Last/@FactorInteger[n]=={1,1}; lst={};Do[If[f[n]&&f[2*n-1]&&f[4*n-3]&&f[8*n-7]&&f[16*n-15]&&f[32*n-31]&&f[64*n-63],AppendTo[lst,n]],{n,0,9!}];lst

%Y Cf. A006881, A177210, A177211, A177212, A177213, A177214.

%K nonn

%O 1,1

%A _Vladimir Joseph Stephan Orlovsky_, May 04 2010

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Last modified December 2 05:01 EST 2021. Contains 349437 sequences. (Running on oeis4.)