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Let nn be the least positive integer such that 168 is a factor of 1134n1134^n. If m is the least positive integer such that 1134n1134^{n}. is a factor of 168m168^m, then m+nm + n equals

Solution

✅ Correct Option: 3

We need to find two values and then add them together.


We need to find the prime factorizations of both numbers to determine divisibility.

For 168:

168=23×31×71168 = 2^3 \times 3^1 \times 7^1

For 1134:

1134=21×34×711134 = 2^1 \times 3^4 \times 7^1

When dealing with factors and multiples, prime factorizations help us see exactly what "ingredients" each number has, making it easy to determine divisibility.


We need 168 to be a factor of 1134n1134^n. In other words, 1134n1134^n must be divisible by 168.

When we raise 1134 to the power n:

1134n=(21×34×71)n=2n×34n×7n1134^n = (2^1 \times 3^4 \times 7^1)^n = 2^n \times 3^{4n} \times 7^n

For 168 to divide 1134n1134^n, we need 1134n1134^n to have at least as many of each prime factor as 168 has.

Comparing the prime factors:

168 needs 232^3, so we need 2n≥232^n \geq 2^3, which means n≥3n \geq 3

168 needs 313^1, so we need 34n≥313^{4n} \geq 3^1, which means 4n≥14n \geq 1, so n≥14n \geq \dfrac{1}{4}

168 needs 717^1, so we need 7n≥717^n \geq 7^1, which means n≥1n \geq 1

The most restrictive condition is n≥3n \geq 3, so n=3n = 3.


Now we need 1134n=113431134^n = 1134^3 to be a factor of 168m168^m.

We have: 11343=23×312×731134^3 = 2^3 \times 3^{12} \times 7^3

When we raise 168 to the power m:

168m=(23×31×71)m=23m×3m×7m168^m = (2^3 \times 3^1 \times 7^1)^m = 2^{3m} \times 3^m \times 7^m

For 113431134^3 to divide 168m168^m, we need 168m168^m to have at least as many of each prime factor as 113431134^3 has.

Comparing the prime factors:

113431134^3 needs 232^3, so we need 23m≥232^{3m} \geq 2^3, which means 3m≥33m \geq 3, so m≥1m \geq 1

113431134^3 needs 3123^{12}, so we need 3m≥3123^m \geq 3^{12}, which means m≥12m \geq 12

113431134^3 needs 737^3, so we need 7m≥737^m \geq 7^3, which means m≥3m \geq 3

The most restrictive condition is m≥12m \geq 12, so m=12m = 12.


m+n=12+3=15m + n = 12 + 3 = 15

When dealing with divisibility problems involving powers, always compare the prime factorizations. The number with fewer factors of any prime will determine the minimum power needed.

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