Is this a puzzle?
Consider the number PowerSmooth(1000000) with the 2 factors removed; e.g. in parigp:
[CODE] PowerSmooth(B1)= result=1; forprime(p=3, B1, result *= p^floor(log(B1)/log(p))); return(result) PowerSmooth(1000000) [/CODE] This number, in binary, has 720737 bits set to 1 ("binary hamming weight", hammingweight() in parigp). The puzzle is: find a multiple of this number that has a Hamming Weight <= 710000. (or, How low a HW multiple can you find?) Thanks! :) 
Iterating thru all odd numbers, starting from 3,
[CODE]3:720673 9:720566 21:720169 59:720143 89:719926 127:719857 237:719477 261:719250 817:719025 6923:718588 229095:718410 276755:718351 322621:718138[/CODE] Using the multiplicative inverse of lower order n bits: [CODE]10:720468 12:719859 242:719603 607:719455 1945:719364 1954:718901 5343:718576[/CODE] Here 5343 means the multiplier is Mod( N, 2^5343)^1 Using random odd numbers < 2^64 [CODE]10719928016004921607:720163 9421399378650073937:719987 9838800997419312683:719646 9031419907504264227:719565 12801182192819992405:719465 11276055256514179587:719415 7687617259492261083:719397 3594335502178041641:719255 6046992651811463807:718858 12624414163832553385:718786 4750919058227643243:718688 18130704136173611049:718654 5224850625010740453:718528 1147537420811012579:718472 7233411429689023907:718469 1993933662070155813:718441 6862363197769235605:718113[/CODE] 
I broke through 718K:
multiplying with 1999099*3684553 produces HW=717965 still a long way to go to 710K.. it looks like the "brute force search" is not working very well. 
Brute force probability analysis.
Hitting < 718K should have a probability around 1 in 2e7, so still achievable by brute force, hitting < 710K is much less likely with 1 in 8e76. Formula used (please correct me if my approach is not applicable):
[$$]p = \frac{\sum_{k=0}^{x}{\binom{\lceil log2(n) \rceil}{k}}}{n}[/$$] [LIST][*][$]p[/$] is the probability.[*][$]n[/$] in the number we want to "depopulize".[*][$]x[/$] is the target popcount. If our target popcount would be greater than [$]\lceil log2(n) \rceil[/$], take the sum from [$]x[/$] to [$]\lceil log2(n) \rceil[/$].[/LIST] Since we are multiplying [$]n[/$] with another value to "depopulize" it, the final result number is getting larger. This is not displayed by this formula, but should not make a huge difference, since our value for multiplication is really small in comparison. 
[QUOTE=kruoli;552531]Hitting < 718K should have a probability around 1 in 2e7, so still achievable by brute force, hitting < 710K is much less likely with 1 in 8e76. Formula used (please correct me if my approach is not applicable):
[$$]p = \frac{\sum_{k=0}^{x}{\binom{\lceil log2(n) \rceil}{k}}}{n}[/$$] [LIST][*][$]p[/$] is the probability.[*][$]n[/$] in the number we want to "depopulize".[*][$]x[/$] is the target popcount. If our target popcount would be greater than [$]\lceil log2(n) \rceil[/$], take the sum from [$]x[/$] to [$]\lceil log2(n) \rceil[/$].[/LIST] Since we are multiplying [$]n[/$] with another value to "depopulize" it, the final result number is getting larger. This is not displayed by this formula, but should not make a huge difference, since our value for multiplication is really small in comparison.[/QUOTE]There appears to be a typo. Should the exceptional sum be taken from 0, not x? 
Do you mean my third bullet point? In that case the sum really should still go from [$]x[/$] to [$]\lceil log2(n) \rceil[/$]. But maybe I'm missing something here. :confused2:

Another possibly interesting question: the quantity hammingweight(PowerSmooth(N))/N appears to converge to a value close to 0.72 can one prove that it converges and can one find a relatively simple expression for its value?

[QUOTE=xilman;552537]Another possibly interesting question: the quantity hammingweight(PowerSmooth(N))/N appears to converge to a value close to 0.72 can one prove that it converges and can one find a relatively simple expression for its value?[/QUOTE]
I assume that half the bits are ones, so that's about equivalent to length of the number x being 1.44N bits, or log(x) = 1.44N*log(2) = N. The prime number theorem says the sum of log(p) for primes p less than L is about L. The PowerSmooth function multiplies the largest power of the prime less than L instead of just the prime itself, but that shouldn't make too much difference. So the 0.72 value is probably 1/log(2)/2, where the 1/log(2) comes from the size of the product as predicted by the prime number theorem, and an additional /2 for only half the bits being ones. 
[QUOTE=xilman;552537]Another possibly interesting question: the quantity hammingweight(PowerSmooth(N))/N appears to converge to a value close to 0.72 can one prove that it converges and can one find a relatively simple expression for its value?[/QUOTE]
This should follow a binomial distributionI suspect. Though no proof as bits are not independent. 
[QUOTE=preda;552502]I broke through 718K:
multiplying with 1999099*3684553 produces HW=717965 still a long way to go to 710K.. it looks like the "brute force search" is not working very well.[/QUOTE] Minor improvements from brute force: [CODE]27275863:717813 93899447:717739[/CODE] 
[CODE]136110417:717547
173564051:717463[/CODE] 
All times are UTC. The time now is 13:55. 
Powered by vBulletin® Version 3.8.11
Copyright ©2000  2020, Jelsoft Enterprises Ltd.