A093625 Primes of the form (3^m + 1)/2.

2, 5, 41, 21523361, 926510094425921, 1716841910146256242328924544641

Offset: 1

Author

Hugo Pfoertner, Apr 19 2004

Keywords

• nonn
• hard

Comments

Primes can only occur for m=2^k. The next term (if it exists) has k >= 21 (i.e., more than 10^6 decimal digits). - Don Reble, Apr 28 2004. [For the latest results about the search, see A171381. - N. J. A. Sloane, Jun 14 2010]

a(7) >= (3^(2^24) + 1)/2, if it exists. - Tyler Busby, Mar 22 2023

Examples

			a(3)=41 because it can be written as (3^4 + 1)/2 = 82/2.
		

Crossrefs

A171381 is the main entry for this sequence. Cf. also A059917, A138083.

Extensions

Erroneous terms deleted by N. J. A. Sloane, Jun 14 2010