• 42 can be written using four 4's:
• Deleting all the even digits from 242 = 4398046511104 we obtain a prime (395111).
42 is nontrivially palindromic in base 4 and base 13.
42 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.
42 is an esthetic number in base 2, because in such base its adjacent digits differ by 1.
It is a sphenic number, since it is the product of 3 distinct primes.
42 is an admirable number.
It is the 5-th Catalan number.
42 is an idoneal number.
42 is an undulating number in base 2.
42 is a nontrivial repdigit in base 4 and base 13.
It is a plaindrome in base 4, base 9, base 11, base 12, base 13, base 15 and base 16.
It is a nialpdrome in base 4, base 6, base 7, base 8, base 10, base 13 and base 14.
It is a zygodrome in base 4 and base 13.
It is a self number, because there is not a number n which added to its sum of digits gives 42.
42 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
42 is a wasteful number, since it uses less digits than its factorization.
42 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 12.
The square root of 42 is about 6.4807406984. The cubic root of 42 is about 3.4760266449.
Adding to 42 its reverse (24), we get a palindrome (66).