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A085721
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Semiprimes whose prime factors have an equal number of digits in binary representation.
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2
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4, 6, 9, 25, 35, 49, 121, 143, 169, 289, 323, 361, 391, 437, 493, 527, 529, 551, 589, 667, 713, 841, 899, 961, 1369, 1517, 1591, 1681, 1739, 1763, 1849, 1927, 1961, 2021, 2173, 2183, 2209, 2257, 2279, 2419, 2491, 2501, 2537, 2623, 2773, 2809
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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LINKS
| Dario A. Alpern, Brilliant Numbers.
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EXAMPLE
| A078972(35) = 527 = 17*31 -> 10001*11111, therefore 527 is a term;
A078972(37) = 533 = 13*41 -> 1101*101001, therefore 533 is not a term;
A001358(1920) = 7169 = 67*107 -> 1000011*1101011: therefore 7169 a term, but not of A078972.
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MATHEMATICA
| fQ[n_] := Block[{fi = FactorInteger@ n}, Plus @@ Last /@ fi == 2 && IntegerLength[ fi[[1, 1]], 2] == IntegerLength[ fi[[-1, 1]], 2]]; Select[ Range@ 2866, fQ] (* Robert G. Wilson v, Oct 29 2011 *)
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PROG
| (PARI) is(n)=bigomega(n)==2&&#binary(factor(n)[1, 1])==#binary(n/factor(n)[1, 1]) \\ Charles R Greathouse IV, Nov 08 2011
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CROSSREFS
| Cf. A078972, A001358, A007088, A070939, A055642.
Sequence in context: A046328 A196104 A046376 * A190300 A081614 A192220
Adjacent sequences: A085718 A085719 A085720 * A085722 A085723 A085724
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KEYWORD
| nonn,base
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AUTHOR
| Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Jul 20 2003
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EXTENSIONS
| Edited by Charles R Greathouse IV (charles.greathouse(AT)case.edu), Aug 02 2010
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