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A059305
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a(n) = pi(Mersenne(n)): index of n-th Mersenne prime.
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24
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OFFSET
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1,1
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COMMENTS
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Similar to A016027, but gives the number of the n-th Mersenne prime (rather than the number of the prime exponent).
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LINKS
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FORMULA
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EXAMPLE
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Element 2 = 4 because Mersenne2 = (2^3)-1 = 7; 7 is the 4th prime.
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MATHEMATICA
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PROG
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(PARI) LL(e) = if(e==2, return(1)); my(n, h); n = 2^e-1; h = Mod(2, n); for (k=1, e-2, h=2*h*h-1); return(0==h) \\ after Joerg Arndt in A000043
forprime(p=1, , if(LL(p), print1(primepi(2^p-1), ", "))) \\ Felix Fröhlich, Apr 19 2019
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CROSSREFS
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KEYWORD
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nonn,hard,more
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AUTHOR
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Reto Keiser (rkeiser(AT)ee.ethz.ch), Jan 25 2001
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EXTENSIONS
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STATUS
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approved
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