66720521 has 16 divisors (see below), whose sum is σ = 77337600. Its totient is φ = 56382480.

The previous prime is 66720491. The next prime is 66720553. The reversal of 66720521 is 12502766.

66720521 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 66720521 - 2¹⁸ = 66458377 is a prime.

It is a super-2 number, since 2×66720521² = 8903255845022882, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (66720721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 293810 + ... + 294036.

It is an arithmetic number, because the mean of its divisors is an integer number (4833600).

Almost surely, 2^66720521 is an apocalyptic number.

It is an amenable number.

66720521 is a deficient number, since it is larger than the sum of its proper divisors (10617079).

66720521 is a wasteful number, since it uses less digits than its factorization.

66720521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 644.

The product of its (nonzero) digits is 5040, while the sum is 29.

The square root of 66720521 is about 8168.2630344523. The cubic root of 66720521 is about 405.5892879624.

The spelling of 66720521 in words is "sixty-six million, seven hundred twenty thousand, five hundred twenty-one".