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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
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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; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| a[ n+1 ]/a[ n ] is very close to 2; a[ n ]/2^n is near to 0.7
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FORMULA
| 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
| 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
| Cf. A000005, A036537, A036539, A037992.
Sequence in context: A054176 A000630 A198486 * A108742 A018240 A090596
Adjacent sequences: A036535 A036536 A036537 * A036539 A036540 A036541
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KEYWORD
| nonn
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu)
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