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A201361
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Numbers k such that (2^k - k + 1)*2^k - 1 is prime.
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7
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1, 2, 3, 8, 14, 35, 75, 83, 89, 90, 215, 342, 753, 1452, 4578, 10337, 25580, 26381
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OFFSET
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1,2
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LINKS
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EXAMPLE
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3 is in the sequence because (2^3 - 3 + 1)*2^3 - 1 = 47 is prime.
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MATHEMATICA
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lst={}; Do[If[PrimeQ[(2^n - n+1)*2^n-1], AppendTo[lst, n]], {n, 10000}]; lst
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PROG
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(Python)
from sympy import isprime
def afind(limit, startk=1):
pow2 = 2**startk
for k in range(startk, limit+1):
if isprime((pow2 - k + 1)*pow2 - 1):
print(k, end=", ")
pow2 *= 2
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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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EXTENSIONS
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STATUS
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approved
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