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A144482 Semiprimes that are a product of Mersenne primes. 6

%I

%S 9,21,49,93,217,381,889,961,3937,16129,24573,57337,253921,393213,

%T 917497,1040257,1572861,3670009,4063201,16252897,16646017,66584449,

%U 67092481,1073602561,4294434817,6442450941,15032385529,17179607041

%N Semiprimes that are a product of Mersenne primes.

%C As the product of any two primes is semiprime by definition, this is also the list of composite numbers n=x*y where both x and y are Mersenne primes. - _Christian N. K. Anderson_, Mar 25 2013

%H Christian N. K. Anderson, <a href="/A144482/b144482.txt">Table of n, a(n) for n = 1..75</a>

%t Take[Times@@@Tuples[2^# -1&/@MersennePrimeExponent[Range[10]],2]//Union,30] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Dec 30 2020 *)

%o (PARI)

%o isA000668(n) = (isprime(n)&&!bitand(n,1+n));

%o isA144482(n) = ((2==bigomega(n))&&isA000668(vecmin(factor(n)[,1]))&&isA000668(vecmax(factor(n)[,1]))); \\ _Antti Karttunen_, Jun 28 2020

%Y Cf. A000668, A001358, A144856, A333788.

%Y Subsequence of A335882.

%K nonn

%O 1,1

%A _G. L. Honaker, Jr._, Oct 12 2008

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Last modified June 19 14:40 EDT 2021. Contains 345140 sequences. (Running on oeis4.)