

A062573


Numbers n such that 7^n  6^n is prime.


4



2, 3, 7, 29, 41, 67, 1327, 1399, 2027, 69371, 86689, 355039
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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^p6^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^n6^n) \\ Charles R Greathouse IV, Feb 20 2017


CROSSREFS

Cf. A000043, A057468, A059801, A059802, A062572A062666.
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. JeanLouis Charton, Oct 06 2010
New term 355039 found by JeanLouis Charton in May 2011 corresponding to a probable prime with 300043 digits.


STATUS

approved



