66640021 has 8 divisors (see below), whose sum is σ = 77203904. Its totient is φ = 56337120.

The previous prime is 66640019. The next prime is 66640043. The reversal of 66640021 is 12004666.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 66640021 - 2¹ = 66640019 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66640061) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 64695 + ... + 65716.

It is an arithmetic number, because the mean of its divisors is an integer number (9650488).

Almost surely, 2^66640021 is an apocalyptic number.

It is an amenable number.

66640021 is a deficient number, since it is larger than the sum of its proper divisors (10563883).

66640021 is a wasteful number, since it uses less digits than its factorization.

66640021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 130491.

The product of its (nonzero) digits is 1728, while the sum is 25.

The square root of 66640021 is about 8163.3339390227. Note that the first 3 decimals coincide. The cubic root of 66640021 is about 405.4261043971.

Adding to 66640021 its reverse (12004666), we get a palindrome (78644687).

The spelling of 66640021 in words is "sixty-six million, six hundred forty thousand, twenty-one".