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 A144856 Semiprimes that are a product of distinct Mersenne primes. 6
 21, 93, 217, 381, 889, 3937, 24573, 57337, 253921, 393213, 917497, 1040257, 1572861, 3670009, 4063201, 16252897, 16646017, 66584449, 1073602561, 4294434817, 6442450941, 15032385529, 66571993057, 68718821377, 272730423169 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Since each Mersenne prime is congruent to -1 (mod 4), it is easy to see that a(n) == 1 (mod 4). - Timothy L. Tiffin, Jul 07 2021 LINKS T. D. Noe, Table of n, a(n) for n = 1..90 G. L. Honaker, Jr. and Chris Caldwell, Prime Curios! 21 Googology Wiki,Largest known squarefree semiprime EXAMPLE a(1) = 3*7 = 21, a(2) = 3*31 = 93, a(3) = 7*31 = 217, ... - Timothy L. Tiffin, Jul 07 2021 MATHEMATICA Mp = 2^{2, 3, 5, 7, 13, 17, 19, 31, 61} - 1; Take[ Union[ Times @@@ Subsets[ Mp, {2}]], 25] (* Robert G. Wilson v, Sep 25 2008 *) CROSSREFS Cf. A000668, A001358. Subsequence of A144482 (semiprimes that are the product of Mersenne primes). Sequence in context: A143843 A119109 A254603 * A065522 A218844 A219423 Adjacent sequences:  A144853 A144854 A144855 * A144857 A144858 A144859 KEYWORD nonn AUTHOR G. L. Honaker, Jr., Sep 22 2008 EXTENSIONS More terms from Robert G. Wilson v, Sep 25 2008 More terms from T. D. Noe, Sep 25 2008 STATUS approved

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Last modified January 24 00:05 EST 2022. Contains 350515 sequences. (Running on oeis4.)