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 A065341 Mersenne composites: 2^prime(m) - 1 is not a prime. 16
 2047, 8388607, 536870911, 137438953471, 2199023255551, 8796093022207, 140737488355327, 9007199254740991, 576460752303423487, 147573952589676412927, 2361183241434822606847, 9444732965739290427391 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 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 A136031. Biggest divisors see A145097. - Artur Jasinski, Oct 01 2008 LINKS Muniru A Asiru, Table of n, a(n) for n = 1..110 FORMULA a(n) = -1 + 2^A054723(n). EXAMPLE 2^11 - 1 = 2047 = 23*89. 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 MATHEMATICA Select[Table[2^Prime[n]-1, {n, 30}], !PrimeQ[#]&] (* Harvey P. Dale, May 06 2018 *) CROSSREFS Cf. A054723, A000043, A000668, A001348. Cf. A135975, A135980, A145097, A136031. - Artur Jasinski, Oct 01 2008 Sequence in context: A069412 A069438 A131952 * A135976 A236373 A289476 Adjacent sequences:  A065338 A065339 A065340 * A065342 A065343 A065344 KEYWORD nonn AUTHOR Labos Elemer, Oct 30 2001 STATUS approved

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Last modified September 24 21:35 EDT 2020. Contains 337322 sequences. (Running on oeis4.)