

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
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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



