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Search: id:A036538
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| A036538 |
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Number of integers m below 2^n such that d(m) = 2^k for some k=0,1,2,3.. |
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+0
1
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| 2, 3, 7, 12, 23, 45, 89, 178, 356, 707, 1409, 2822, 5639, 11273, 22546, 45088, 90165, 180315, 360637
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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a[ n+1 ]/a[ n ] is very close to 2; a[ n ]/2^n is near to 0.7
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FORMULA
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bi[ x_ ] := 1-Sign[ N[ Log[ 2, x ], 5 ]-Floor[ N[ Log[ 2, x ], 5 ] ] ], ld[ x_ ] := Length[ Divisors[ x ] ], Table[ Length[ Flatten[ Position[ Table[ bi[ ld[ x ] ], {x, 1, 2^m} ], 1 ] ] ], {m, 1, 19} ]
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EXAMPLE
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From numbers not exceeding 16=2^4, only 4,9,12 and 16 are not in the sequence, so a[ 4 ]=16-4=12
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CROSSREFS
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Cf. A000005, A036537, A036539, A037992.
Adjacent sequences: A036535 A036536 A036537 this_sequence A036539 A036540 A036541
Sequence in context: A027675 A054176 A000630 this_sequence A108742 A018240 A090596
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KEYWORD
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nonn
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AUTHOR
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Labos E. (labos(AT)ana.sote.hu)
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