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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
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
G. L. Honaker, Jr. and Chris Caldwell, Prime Curios! 21
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
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