That depends on where you start and in what direction you proceed. If you list the prime factors in the order from smallest to largest, then the first two are 2 and 3, and their sum is 5.
The sum of the two largest prime numbers less than 71 is 128.
5
The largest prime less than 20 is 19. The largest prime over 60 is 61. The sum of these two numbers is 80.
78
269
The sum of the factors of 2^16 - 1 = 65535 is 299.
They are: 89+97 = 186
The largest factor that 12 and 30 have in common is the product of the two prime factors they have in common.
17, 23.
42 has three prime factors: 2, 3 and 7
Mostly yes, but not always.