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A138025
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Numbers n such that n remains prime through 7 iterations of function f(x) = 2x + 1.
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1
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19099919, 52554569, 85864769, 171729539, 198479579, 226366139, 305192579, 344319029, 396959159, 474118349, 574964129, 610385159, 685066979, 764406059, 1085182229, 1126004219, 1195651139, 1372213439, 1484454269, 1573750049, 2270291519, 2365144079, 2400025739
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OFFSET
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1,1
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COMMENTS
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n, 2*n+1, 4*n+3, 8*n+7, 16*n+15, 32*n+31, 64*n+63, and 128*n+127 are primes. - John Cerkan, Dec 04 2016
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LINKS
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FORMULA
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MATHEMATICA
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Select[Prime[Range[10^7]], PrimeQ[a1=2*#+1]&&PrimeQ[a2=2*a1+1]&&PrimeQ[a3=2*a2+1]&&PrimeQ[a4=2*a3+1]&&PrimeQ[a5=2*a4+1]&&PrimeQ[a6=2*a5+1]&&PrimeQ[a7=2*a6+1] &]
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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