5 20 380 144020 ?
"if number = n , then next number = n * ( n - 1 ) so 5 , ( 5 * 4 = 20 ) , ( 20 * 19 = 380 ) , ( 380 * 379 = 144020 ) , ( 144020 * 144019 = 20741616380 ) answer : a"
divide(multiply(add(5, divide(20, 380)), 144020), const_100)