if { x } is the product of all even integers from 1 to x inclusive , what is the greatest prime factor of { 20 } + { 24 } ?
"soln : { 24 } + { 20 } = 24 * { 20 } + { 20 } = 25 * { 20 } answer : b"
add(divide(add(20, 24), const_2), multiply(1, const_2))