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 A172315 Primes of the form 2^i*3^j - 1 with i + j = 13. 1
 8191, 27647, 62207, 139967, 314927, 472391, 1062881 (list; graph; refs; listen; history; text; internal format)
 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 LINKS 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 Cf. A005105, A168385, A168349 Sequence in context: A108093 A051334 A145592 * A103902 A075960 A011563 Adjacent sequences:  A172312 A172313 A172314 * A172316 A172317 A172318 KEYWORD fini,full,nonn AUTHOR Eva-Maria Zschorn (e-m.zschorn(AT)zaschendorf.km3.de), Jan 31 2010 STATUS approved

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