66605721 has 64 divisors (see below), whose sum is σ = 116121600. Its totient is φ = 33014016.

The previous prime is 66605713. The next prime is 66605761. The reversal of 66605721 is 12750666.

It is not a de Polignac number, because 66605721 - 2³ = 66605713 is a prime.

It is not an unprimeable number, because it can be changed into a prime (66605761) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 372010 + ... + 372188.

It is an arithmetic number, because the mean of its divisors is an integer number (1814400).

Almost surely, 2^66605721 is an apocalyptic number.

It is an amenable number.

66605721 is a deficient number, since it is larger than the sum of its proper divisors (49515879).

66605721 is a wasteful number, since it uses less digits than its factorization.

66605721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 278.

The product of its (nonzero) digits is 15120, while the sum is 33.

The square root of 66605721 is about 8161.2328112853. The cubic root of 66605721 is about 405.3565340813.

The spelling of 66605721 in words is "sixty-six million, six hundred five thousand, seven hundred twenty-one".