A095027 Semiprimes of the form 3^n - 2^n.

65, 2059, 19171, 1586131, 1161737179, 94134790219, 450283768452043891, 7509466514977363620705281135650699, 2909321189362570189660446183802104997118371, 19088056323407826916968161259086927505582748291

Offset

1,1

Links

Table of n, a(n) for n=1..10.

Dario Alpern, Factorization using the Elliptic Curve Method

Example

a(1)=65 because 3^4-2^4=65=5*13 is a semiprime; a(3)=19171: 3^9-2^9=19171=19*1009.

Mathematica

Select[Table[3^n - 2^n, {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 3^n - 2^n]; // Vincenzo Librandi, Sep 21 2012

Crossrefs

Cf. A082869 = n such that 3^n-2^n is a semiprime, A058765 primes of the form 3^n-2^n.

Sequence in context: A031604 A002502 A333118 * A017781 A017728 A300168

Adjacent sequences: A095024 A095025 A095026 * A095028 A095029 A095030

Keyword

nonn

Author

Hugo Pfoertner, Jun 03 2004

Extensions

a(10) from Vincenzo Librandi, Sep 21 2012

Status

approved