#(7!)/((2!)^3) = 630#
#"In general when we arrange n items, where there are k different"#
#"items that occur each "n_i" times, for "i=1,2,...,k", then we"#
#"have"#
#(n!)/((n_1)!(n_2)!...(n_k)!)#
#"possibilities of arranging them."#
#"So we need to count how many times the items occur :"#
#"Here we have 7 items : two 579 and one 6, so"#
#(7!)/(2!2!2!1!) = 630 " possibilities"#
#"This is called a multinomial coefficient."#
#"The philosophy behind it is simple. We would have n! ways of"#
#"arranging them if they were different, but the identical items"#
#"can be arranged in "n_i!" ways, without affecting the outcome"#
#"so we divide through all the "(n_i)!.#