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A233089
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Numbers n such that 2n-1 and 2n+1 divide 2^n-1.
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1
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8, 128, 228, 648, 3240, 5976, 13160, 23760, 23940, 24840, 32768, 37224, 78540, 82800, 139248, 166716, 238368, 278520, 280368, 288360, 516528, 633420, 664668, 731808, 734448, 1145520, 1211100, 1377240, 1425816, 1484568, 1627640, 2055060, 2131080, 2292780
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OFFSET
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1,1
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COMMENTS
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LINKS
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EXAMPLE
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2^8-1=255 is divisible by 2*8-1=15 and by 2*8+1=17.
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MATHEMATICA
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Select[Range[23*10^5], PowerMod[2, #, 2#+{1, -1}]=={1, 1}&] (* Harvey P. Dale, Dec 19 2014 *)
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PROG
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(PARI) isok(n) = !((2^n-1) % (2*n-1)) && !((2^n-1) % (2*n+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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STATUS
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approved
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