There 25 primes less than 100: 2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97.
The two-digit primes less than 50 are 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, and 47. For each prime on this list whose tens digit is odd, check whether or not the number formed when the digits are reversed is also prime. (Note that if the tens digit is even, then the ``reversed'' number is even and hence not prime.) The palindromic primes less than 50 are 11, 13, 17, 31, and 37, whose sum is 109.
The odd primes less than 20 are: 3 5 7 11 13 17 19
59 and 53 are the two largest primes less than 60. 59+53 = 112
There are 168 prime numbers less than 1,000.
37 and 79
There are 8 twin primes less than 100. 3,5 : 5,7 : 11,13 : 17,19 : 29,31 : 41,43 : 59,61 : 71,73
here are all 8, 3,5 11,13 17,19 59,61 29,31 41,43 5,7 71,73
To find how many numbers less than 100 are the product of 3 distinct primes, we can consider combinations of distinct primes. The smallest three distinct primes are 2, 3, and 5, whose product is 30. The next combination, 2, 3, and 7, gives 42, and continues with combinations like 2, 5, and 7 (70) and 3, 5, and 7 (105, which exceeds 100). Thus, the valid products less than 100 are 30, 42, and 70, leading to a total of 3 such numbers.
The median of the 12 primes less than 40 is 15.
9.
eight (8)