A156555 Primes of the form 3^k - 4.

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

Offset

1,1

Comments

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

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

Formula

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

Example

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

Mathematica

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

Prog

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

Crossrefs

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

Sequence in context: A322238 A295080 A323993 * A361403 A116652 A361362

Adjacent sequences: A156552 A156553 A156554 * A156556 A156557 A156558

Keyword

nonn

Author

Vincenzo Librandi, Feb 10 2009

Extensions

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

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

Status

approved