A198725 Primes of the form (6^n-11)/5.

5, 41, 257, 1553, 15672832817, 121871948002097, 4387390128075569, 161656255492952812128627920091307258673, 34917751186477807419783630739722367873841

Offset: 1

Author

Gilbert Mozzo, Oct 29 2011

Keywords

• nonn

Comments

These primes are also given by sum 6^k -1 with k>0 and are then companions of A165210 which corresponds also to sum 6^k +1 with k>0. (Be careful: there is a shifting between the k and the n values).

Corresponding exponents n are in A199165. - Gilbert Mozzo, Nov 05 2011

Examples

			(6^4-11)/5=257, which is in the sequence because it is prime.
		

Crossrefs

Cf. A165210, A004062, A199165.

Programs

Magma

[(6^n-11)/5: n in [1..10^3] | IsPrime((6^n-11) div 5)];

Mathematica

lst={}; Do[If[PrimeQ[(6^n-11)/5], Print[(6^n-11)/5]; AppendTo[lst, (6^n-11)/5]], {n, 10^6}];

PARI

for(n=1,1e4,if(ispseudoprime(t=6^n\5-2),print1(t", "))) \\ Charles R Greathouse IV, Nov 01 2011