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A144482 Semiprimes that are a product of Mersenne primes. 6
9, 21, 49, 93, 217, 381, 889, 961, 3937, 16129, 24573, 57337, 253921, 393213, 917497, 1040257, 1572861, 3670009, 4063201, 16252897, 16646017, 66584449, 67092481, 1073602561, 4294434817, 6442450941, 15032385529, 17179607041 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

LINKS

Christian N. K. Anderson, Table of n, a(n) for n = 1..75

MATHEMATICA

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

PROG

(PARI)

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

isA144482(n) = ((2==bigomega(n))&&isA000668(vecmin(factor(n)[, 1]))&&isA000668(vecmax(factor(n)[, 1]))); \\ Antti Karttunen, Jun 28 2020

CROSSREFS

Cf. A000668, A001358, A144856, A333788.

Subsequence of A335882.

Sequence in context: A160414 A256530 A118130 * A251212 A176896 A134717

Adjacent sequences:  A144479 A144480 A144481 * A144483 A144484 A144485

KEYWORD

nonn

AUTHOR

G. L. Honaker, Jr., Oct 12 2008

STATUS

approved

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Last modified May 17 16:03 EDT 2021. Contains 343980 sequences. (Running on oeis4.)