• 66 can be written using four 4's:
• Sorting the digits of 266 in ascending order we obtain a prime of 19 digits.
66 is the minimal such that the integers from 1 to
can be arranged in a circle so that the sum of two adjacent
terms is a palindrome with at least 2 digits:
66 is nontrivially palindromic in base 10.
66 is an esthetic number in base 7 and base 12, because in such bases its adjacent digits differ by 1.
It is a sphenic number, since it is the product of 3 distinct primes.
66 is an admirable number.
It is a nude number because it is divisible by every one of its digits.
66 is a nontrivial repdigit in base 10.
It is a plaindrome in base 7, base 10, base 12, base 14 and base 15.
It is a nialpdrome in base 3, base 9, base 10, base 11, base 13 and base 16.
It is a zygodrome in base 10.
It is equal to the Eulerian number A(5, 2).
66 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.
66 is a wasteful number, since it uses less digits than its factorization.
66 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 16.
The square root of 66 is about 8.1240384046. The cubic root of 66 is about 4.0412400206.
Adding to 66 its sum of digits (12), we get a triangular number (78 = T12).