+134 So you have to find the lagest prime number under 28, beacuse if you multiple 2 numbers, even if they are prime, you will get a compostie number. And we know that the largest prime number less than 28 is 23, so from here the answere is 23.
+310 Since both have 27 factorial, we can factorize to get 27! (1+28) = 27! * 29.
The largest prime that divides 27! + 28! is 29.
+310 28! means 28 factorial which is 28*27*26...*1.
27! is 27*26*25...*1.
So we can take out 27!.
