66612721 has 16 divisors (see below), whose sum is σ = 77670400. Its totient is φ = 55952208.

The previous prime is 66612703. The next prime is 66612731. The reversal of 66612721 is 12721666.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 66612721 - 2¹³ = 66604529 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66612701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 89770 + ... + 90508.

It is an arithmetic number, because the mean of its divisors is an integer number (4854400).

Almost surely, 2^66612721 is an apocalyptic number.

It is an amenable number.

66612721 is a deficient number, since it is larger than the sum of its proper divisors (11057679).

66612721 is a wasteful number, since it uses less digits than its factorization.

66612721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 988.

The product of its digits is 6048, while the sum is 31.

The square root of 66612721 is about 8161.6616567951. The cubic root of 66612721 is about 405.3707340444.

The spelling of 66612721 in words is "sixty-six million, six hundred twelve thousand, seven hundred twenty-one".