A092562 Semiprimes of the form 2^k + 1.

9, 33, 65, 129, 2049, 4097, 8193, 131073, 524289, 1048577, 8388609, 268435457, 2147483649, 4294967297, 1099511627777, 8796093022209, 2305843009213693953, 18446744073709551617, 604462909807314587353089, 4951760157141521099596496897

Offset: 1

Author

Zak Seidov, Feb 27 2004

Keywords

• nonn

Examples

			2049 is a member because 2049 = 2^11+1 = 3*683.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..40 (terms 1..30 from Vincenzo Librandi)

Crossrefs

Corresponding k: A092559.

Cf. A000051, A092558, A092561.

Programs

Magma

IsSemiprime:=func; [s: n in [2..100] | IsSemiprime(s) where s is 2^n+1]; // Vincenzo Librandi, Sep 21 2012

Mathematica

Select[Table[2^n + 1, {n, 100}], PrimeOmega[#] == 2&] (* Vincenzo Librandi, Sep 21 2012 *)

Formula

a(n) = A000051(A092559(n)). - Amiram Eldar, Jun 18 2022