49

49 is a perfect square: 49 = 7² . It is the first square whose digits are square.

49 is the smallest number with the property that it and its neighbors are squareful. In other words, each of these numbers contains at least one square in its factorization.

48 = 2² x 2² x 3
49 = 7²
50 = 2 x 5²

49 is the smallest composite number that is not divisible by any Fibonacci number greater than 1.

49 has a unique representation as a sum of three squares: 49 = 2² + 3² + 6².

49 is the smallest number with exactly eight representations as a sum of three distinct primes: 49 = 3 + 5 + 41 = 3 + 17 + 29 = 5 + 7 + 37 = 5 + 13 + 31 = 7 + 11 + 31 = 7 + 13 + 29 = 7 + 19 + 23 = 13 + 17 + 19.

49 is the atomic number of the element indium.

Source: Number Gossip