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A065341
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Mersenne composites: 2^prime(n) - 1 is not a prime.
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12
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2047, 8388607, 536870911, 137438953471, 2199023255551, 8796093022207, 140737488355327, 9007199254740991, 576460752303423487, 147573952589676412927, 2361183241434822606847, 9444732965739290427391
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Number of prime factors in a(n) see A135975. Indices of primes n in composite 2^Prime[n]-1 see A135980. Smallest prime divisors of Mersenne composites see A136030. Biggest prime divisors of Mersenne composites see A145098 Biggest divisors see A145097. [From Artur Jasinski (grafix(AT)csl.pl), Oct 01 2008]
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FORMULA
| a(n)=-1+2^A054723(n)
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EXAMPLE
| 2047=23.89
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MAPLE
| A065341 := proc(n) local i;
i := 2^(ithprime(n))-1:
if (not isprime(i)) then
RETURN (i)
fi: end: seq(A065341(n), n=1..21); # - Jani Melik, Feb 09 2011
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MATHEMATICA
| a = {}; Do[m = 2^Prime[n] - 1; If[PrimeQ[m], NULL, AppendTo[a, m]], {n, 1, 20}]; a [From Artur Jasinski (grafix(AT)csl.pl), Oct 01 2008]
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CROSSREFS
| Cf. A054723, A000043, A000668, A001348
A135975, A135980, A145097, A145098 [From Artur Jasinski (grafix(AT)csl.pl), Oct 01 2008]
Sequence in context: A069412 A069438 A131952 * A135976 A035892 A069272
Adjacent sequences: A065338 A065339 A065340 * A065342 A065343 A065344
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KEYWORD
| nonn
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Oct 30 2001
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