A prime factorisation of a natural number can be expressed in the exponential form. For example: (i) 48 = 2×2×2×2×3 = 24×3 (ii) 420 = 2×2×3×5×7 = 2² ×3×5×7. Least Common Multiple (abbreviated L.C.M.) of two natural numbers is the smallest natural number which is a multiple of both the numbers. Highest Common Factor (abbreviated H.C.F.) of two natural numbers is the largest common factor (or divisor) of the given natural numbers. In other words, H.C.F. is the greatest element of the set of common factors of the given numbers. H.C.F. is also called Greatest Common Divisor (abbreviated G.C.D.)