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Question

What is the sum of all the divisors of 256 ?

This question was previously asked in
CDS 2 2026 Maths Question Paper (13-Sep-2026)
The correct answer is
511

The question asks for the sum of all the divisors of the number 256.

Divisors Calculation for 256

First, find the prime factorization of 256.

256 is a power of 2:

\(256 = 2^8\)

Sum of Divisors Formula

For a number \(N\) expressed as a product of prime factors \(N = p_1^{a_1} p_2^{a_2} ... p_k^{a_k}\), the sum of its divisors, denoted by \(\sigma(N)\), is calculated using the formula:

\(\sigma(N) = \left(\frac{p_1^{a_1+1}-1}{p_1-1}\right) \times \left(\frac{p_2^{a_2+1}-1}{p_2-1}\right) \times ... \times \left(\frac{p_k^{a_k+1}-1}{p_k-1}\right)\)

In the case of 256, we have only one prime factor, \(p_1 = 2\), and its exponent is \(a_1 = 8\). So, \(N = 2^8\).

Applying the Formula

Substitute the values into the formula:

\(\sigma(256) = \sigma(2^8) = \frac{2^{8+1}-1}{2-1}\)

Simplify the expression:

\(\sigma(2^8) = \frac{2^9-1}{1}\)

\(\sigma(2^8) = 2^9 - 1\)

Final Calculation

Calculate the value of \(2^9\):

\(2^9 = 512\)

Now, subtract 1:

\(\sigma(256) = 512 - 1 = 511\)

The sum of all the divisors of 256 is 511.

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