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If underset(r=1)overset(n)sum [log(2) r...

If `underset(r=1)overset(n)sum [log_(2) r]=2010` where [.] denotes greatest integer function, then the sum of the digits of n is:

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To solve the problem, we need to evaluate the summation of the greatest integer function of logarithm base 2 from \( r = 1 \) to \( n \) and set it equal to 2010. ### Step-by-Step Solution: 1. **Understanding the Summation**: We need to evaluate: \[ \sum_{r=1}^{n} \lfloor \log_2 r \rfloor = 2010 \] The function \( \lfloor \log_2 r \rfloor \) gives the greatest integer less than or equal to \( \log_2 r \). This function changes its value at powers of 2. 2. **Identifying the Values of \( \lfloor \log_2 r \rfloor \)**: - For \( r = 1 \): \( \lfloor \log_2 1 \rfloor = 0 \) - For \( r = 2, 3 \): \( \lfloor \log_2 r \rfloor = 1 \) - For \( r = 4, 5, 6, 7 \): \( \lfloor \log_2 r \rfloor = 2 \) - For \( r = 8, 9, 10, 11, 12, 13, 14, 15 \): \( \lfloor \log_2 r \rfloor = 3 \) - For \( r = 16, 17, \ldots, 31 \): \( \lfloor \log_2 r \rfloor = 4 \) - And so on... 3. **Counting Contributions**: The contributions to the sum can be counted based on the ranges defined by powers of 2: - From \( 1 \) to \( 1 \): contributes \( 0 \times 1 = 0 \) - From \( 2 \) to \( 3 \): contributes \( 1 \times 2 = 2 \) - From \( 4 \) to \( 7 \): contributes \( 2 \times 4 = 8 \) - From \( 8 \) to \( 15 \): contributes \( 3 \times 8 = 24 \) - From \( 16 \) to \( 31 \): contributes \( 4 \times 16 = 64 \) - From \( 32 \) to \( 63 \): contributes \( 5 \times 32 = 160 \) - From \( 64 \) to \( 127 \): contributes \( 6 \times 64 = 384 \) - From \( 128 \) to \( 255 \): contributes \( 7 \times 128 = 896 \) - From \( 256 \) to \( 511 \): contributes \( 8 \times 256 = 2048 \) (but we will not reach this far since we need to total 2010) 4. **Summing Contributions**: Now we sum these contributions until we reach or exceed 2010: \[ 0 + 2 + 8 + 24 + 64 + 160 + 384 + 896 = 1534 \] This means we have accounted for \( 1534 \) up to \( r = 255 \). 5. **Finding Remaining Value**: We need to reach \( 2010 \): \[ 2010 - 1534 = 476 \] Now, for \( r = 256 \) and onwards, \( \lfloor \log_2 r \rfloor = 8 \). 6. **Calculating Additional Terms**: We can add \( 8 \) for each additional \( r \): \[ 8k = 476 \implies k = \frac{476}{8} = 59.5 \] Since \( k \) must be an integer, we can only take \( k = 59 \) which gives: \[ 8 \times 59 = 472 \] Thus, we can take \( r \) from \( 256 \) to \( 314 \) (59 terms). 7. **Finding \( n \)**: Therefore, \( n = 255 + 59 = 314 \). 8. **Sum of Digits of \( n \)**: Now, we find the sum of the digits of \( n = 314 \): \[ 3 + 1 + 4 = 8 \] ### Final Answer: The sum of the digits of \( n \) is \( \boxed{8} \).
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