

A063679


Numbers n such that (3^n7)/2 is prime.


2



4, 12, 18, 26, 106, 164, 246, 956, 2554, 3350, 6496, 8706, 9008
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OFFSET

1,1


COMMENTS

x = 3^n is a solution to sigma(x  7) = sigma(x)  7 when (3^n  7)/2 is prime.


LINKS

Table of n, a(n) for n=1..13.


EXAMPLE

(3^47)/2 = 37 is prime, so 4 is in the sequence.


MAPLE

with(numtheory):i := 0:x := 1:while i < 1000 do i := i+1:x := 3*x: if isprime((x7)/2) then print(i):fi:od:


MATHEMATICA

Do[ If[ PrimeQ[ (3^n  7)/2 ], Print[n] ], {n, 2, 5500} ]
Select[Range[2, 10000], PrimeQ[((3^#  7)/2)] &] (* Vincenzo Librandi, Sep 30 2012 *)


PROG

(PARI) is(n)=ispseudoprime((3^n7)/2) \\ Charles R Greathouse IV, May 22 2017


CROSSREFS

Cf. A000203, A063680, A015913A015917, A054905.
Sequence in context: A074285 A301252 A057311 * A075867 A071929 A008037
Adjacent sequences: A063676 A063677 A063678 * A063680 A063681 A063682


KEYWORD

nonn


AUTHOR

Jud McCranie, Jul 28 2001


EXTENSIONS

More terms from Robert G. Wilson v, Aug 02 2001
0, 1 removed and a(11)a(13) added from Vincenzo Librandi, Sep 30 2012


STATUS

approved



