A156555 Primes of the form 3^k - 4.

5, 23, 239, 10460353199, 617673396283943, 450283905890997359, 36472996377170786399, 19383245667680019896796719, 67585198634817523235520443624317919, 1546132562196033993109383389296863818106322565999

Offset: 1

Author

Vincenzo Librandi, Feb 10 2009

Keywords

• nonn

Comments

The next term, a(11), has 84 digits. - Harvey P. Dale, Jul 24 2011

Examples

			a(1) = 3^2 - 4 = 5 is the smallest prime of that form. - _M. F. Hasler_, Oct 31 2009
		

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..17
• F. Firoozbakht, M. F. Hasler, Variations on Euclid's formula for Perfect Numbers, JIS 13 (2010) #10.3.1
• Henri & Renaud Lifchitz, PRP Records
• OpenPFGW Project, Primality Tester

Crossrefs

Cf. A000040, A058959 (corresponding k's).

Programs

Mathematica

Select[3^Range[200]-4,PrimeQ] (* Harvey P. Dale, Jul 24 2011 *)

PARI

for( k=2,999, is/*pseudo*/prime( p=3^k-4 ) & print1(p", ")) \\ M. F. Hasler, Oct 31 2009

Formula

a(n) = 3^A058959(n) - 4. - M. F. Hasler, Oct 31 2009

Extensions

a(5) corrected by M. F. Hasler, Oct 31 2009

a(10) from Harvey P. Dale, Jul 24 2011