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A200878
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Composite numbers whose prime factors have equal numbers of bits.
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2
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4, 6, 8, 9, 12, 16, 18, 24, 25, 27, 32, 35, 36, 48, 49, 54, 64, 72, 81, 96, 108, 121, 125, 128, 143, 144, 162, 169, 175, 192, 216, 243, 245, 256, 288, 289, 323, 324, 343, 361, 384, 391, 432, 437, 486, 493, 512, 527, 529, 551, 576, 589, 625, 648, 667, 713
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OFFSET
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1,1
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LINKS
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EXAMPLE
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7429 = 17*19*23 -> 10001*10011*10111, therefore 7429 is a term.
7430 = 2*5*743 -> 10*101*1011100111, therefore 7430 is not a term.
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MATHEMATICA
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lst = {}; Do[b = IntegerDigits[FactorInteger[n], 2]; If[! PrimeQ[n] && Length[b[[-1, 1]]] == Length[b[[1, 1]]], AppendTo[lst, n]], {n, 4, 6!}]; lst (* Arkadiusz Wesolowski, Dec 03 2011 *)
Select[Range[800], CompositeQ[#]&&Length[Union[IntegerLength[ #, 2]&/@ FactorInteger[ #][[All, 1]]]]==1&] (* Harvey P. Dale, Oct 11 2021 *)
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PROG
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(PARI) is(n)=my(f=factor(n)[, 1]); #binary(f[1])==#binary(f[#f])&&!isprime(n) \\ Charles R Greathouse IV, Dec 23 2011
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CROSSREFS
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KEYWORD
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base,nonn
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AUTHOR
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STATUS
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approved
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