A062573 Numbers k such that 7^k - 6^k is prime.

2, 3, 7, 29, 41, 67, 1327, 1399, 2027, 69371, 86689, 355039

Offset

1,1

Comments

Terms greater than 1000 often correspond only to strong probable primes.

Links

Table of n, a(n) for n=1..12.

Henri & Renaud Lifchitz, Top probable primes of the form 7^p-6^p

Example

7^2 - 6^2 = 49 - 36 = 13, which is prime, so 2 is in the sequence.
7^3 - 6^3 = 343 - 216 = 127, which is prime, so 3 is in the sequence.

Mathematica

Select[Range[100], PrimeQ[7^# - 6^#] &] (* Alonso del Arte, Sep 04 2013 *)

Prog

(PARI) is(n)=ispseudoprime(7^n-6^n) \\ Charles R Greathouse IV, Feb 20 2017

Crossrefs

Cf. A000043, A057468, A059801, A059802, A062572-A062666.

Sequence in context: A270347 A060412 A276665 * A019435 A061092 A084435

Adjacent sequences: A062570 A062571 A062572 * A062574 A062575 A062576

Keyword

nonn,hard

Author

Mike Oakes, May 18 2001, May 19 2001

Extensions

Two more terms (69371 and 86689) found by Predrag Minovic in 2004 corresponding to probable primes with 58626 and 73261 digits. - Jean-Louis Charton, Oct 06 2010

New term 355039 found by Jean-Louis Charton in May 2011 corresponding to a probable prime with 300043 digits.

Status

approved