A144856 Semiprimes that are a product of distinct Mersenne primes.

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

Author

G. L. Honaker, Jr., Sep 22 2008

Keywords

• nonn

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

Examples

			a(1) = 3*7 = 21, a(2) = 3*31 = 93, a(3) = 7*31 = 217, ... - _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

Crossrefs

Cf. A000668, A001358. Subsequence of A144482 (semiprimes that are the product of Mersenne primes).

Programs

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 *)

Extensions

More terms from Robert G. Wilson v, Sep 25 2008

More terms from T. D. Noe, Sep 25 2008