LCM for 21 and 42

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What's the Least Common Multiple (LCM) of 21 and 42?

Answer

LCM of 21 and 42 is
42

First common multiples: 42, 84, 126, …

As a common denominator: multiply the top and bottom of x/21 by 2.

21 divides 42 (42 ÷ 21 = 2), so the LCM is the larger number itself.

21 = 3 × 7

42 = 2 × 3 × 7

Prime2142Highest power
2—22
3333
7777

— = power 0: the prime is not a factor of this number; the LCM takes it from the number that has it.

LCM = 2 × 3 × 7 = 42

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LCM Table

Number 1Number 2LCM
2123483
2124168
2125525
2126546
212884
2129609
2130210
2132672
2133231
2134714
2135105
2136252
2139273
2140840
2141861
214242
2143903
2144924
2145315
2146966
2147987
2148336
2149147
2151357
21521,092
21531,113
2156168
21581,218
21591,239
2160420

FAQ

What's the Least Common Multiple (LCM) of 21 and 42?

LCM of 21 and 42 is 42

How to find the LCM of 21 and 42 using prime factorization?

To find the LCM of 21 and 42, find all prime factors of both numbers, then multiply the highest power of each prime factor. The result is 42.

What is the difference between LCM and GCF?

LCM (Least Common Multiple) is the smallest number divisible by both numbers, while GCF (Greatest Common Factor) is the largest number that divides both. For 21 and 42: LCM = 42, GCF = 21.

See Also