• 65 can be written using four 4's:
65 is nontrivially palindromic in base 2, base 4, base 8 and base 12.
65 is an esthetic number in base 8, base 10 and base 15, because in such bases its adjacent digits differ by 1.
It is a semiprime because it is the product of two primes.
It is a cyclic number.
It is a Cullen number, since it is equal to 4×24+1.
65 is a rare number.
It is a magnanimous number.
It is an alternating number because its digits alternate between even and odd.
It is a Duffinian number.
65 is an undulating number in base 8.
It is a Curzon number.
65 is a nontrivial repdigit in base 12.
It is a plaindrome in base 6, base 7, base 11, base 12, base 14 and base 15.
It is a nialpdrome in base 9, base 10, base 12, base 13 and base 16.
It is a zygodrome in base 12.
It is a congruent number.
It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 65.
65 is the 5-th octagonal number.
It is an amenable number.
65 is a wasteful number, since it uses less digits than its factorization.
65 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 18.
The square root of 65 is about 8.0622577483. The cubic root of 65 is about 4.0207257586.
Adding to 65 its reverse (56), we get a palindrome (121).