Positive integers

How many positive integers n n have the property that the remainder of dividing 2003 by n n is equal to 23?


The answer is 22.

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2 solutions

Munem Shahriar
May 12, 2017

If 2003 is divided by n, the result would be a whole number 'N' plus a remainder.

If the remainder is 23, then,

2003 n \frac{2003}{n} = N + 23 n \frac{23}{n}

or, N = 1980 n \frac{1980}{n}

or, n = 1980 N \frac{1980}{N}

The factors of 1980,

1, 2, 3, 4, 5, 6, 9, 10, 11, 12, 15, 18, 20, 22, 30, 33, 36, 44, 45, 55, 60, 66, 90, 99, 110, 132, 165, 180, 198, 220, 330, 396, 495, 660, 990 and 1980

n must be greater than 23 [ otherwise the remainder cannot be 23 ]

Therefore, there are 22 possible values of n = 30, 33, 36, 44, 45, 55, 60, 66, 90, 99, 110, 132, 165, 180, 198, 220, 330, 396, 495, 660, 990 and 1980

Answer : 22

Tapas Mazumdar
May 14, 2017

2003 23 ( m o d n ) 2003 23 0 ( m o d n ) 1980 0 ( m o d n ) 2003 \equiv 23 \pmod{n} \\ \implies 2003 - 23 \equiv 0 \pmod{n} \\ \implies 1980 \equiv 0 \pmod{n}

Thus n n should be a divisor of 1980 1980 . Also note that n > 23 n > 23 to give a remainder of 23 23 when it divides 2003 2003 .

Prime factorization of 1980 1980 gives 1980 = 2 2 × 3 2 × 5 × 11 1980 = 2^2 \times 3^2 \times 5 \times 11 . Thus 1980 1980 has 36 36 divisors. Listing out the divisors, we find that there are 14 14 divisors which are less than 23 23 , so our required answer is 36 14 = 22 36 - 14 = \boxed{22} .

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