OFFSET
1,1
COMMENTS
Note that bases 2 = prime(1), 3 = prime(2)
13 = prime(2 x 3) = prime(prime(1) x prime(2))
Smallest term 8191 is the 5th Mersenne prime
It is a finite "FUN" sequence with 7 = prime(4) terms
REFERENCES
Helmut Kracke, Mathe-musische Knobelisken, Duemmler Bonn, 2. Auflage 1983
EXAMPLE
8191 = 2^13 - 1 = prime(1028)
27647 = 2^10 x 3^3 - 1 = prime(3016) = prime(2^3 x 13 x 29)
62207 = 2^8 x 3^5 - 1 = prime(6253) = prime(13^ 2 x 37)
139967 = 2^6 x 3^7 - 1 = prime(13005)
314927 = 2^4 x 3^9 - 1 = prime(27191), index is prime(2978)
472391 = 2^3 x 3^10 - 1 = prime(39419), index is prime(4150)
1062881 = 2 x 3^12 - 1 = prime(83024)
MATHEMATICA
Select[Union[Flatten[{2^#[[1]] 3^#[[2]]-1, 2^#[[2]] 3^#[[1]]-1}&/@ Table[ {n, 13-n}, {n, 0, 13}]]], PrimeQ] (* Harvey P. Dale, Jan 11 2016 *)
CROSSREFS
KEYWORD
fini,full,nonn
AUTHOR
Eva-Maria Zschorn (e-m.zschorn(AT)zaschendorf.km3.de), Jan 31 2010
STATUS
approved