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

1,1

Links

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

Formula

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

Example

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

Mathematica

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

Prog

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

Crossrefs

Corresponding k: A092559.

Cf. A000051, A092558, A092561.

Sequence in context: A046895 A165392 A145923 * A103602 A205796 A081585

Adjacent sequences: A092559 A092560 A092561 * A092563 A092564 A092565

Keyword

nonn

Author

Zak Seidov, Feb 27 2004

Status

approved