66638921 has 4 divisors (see below), whose sum is σ = 66831312. Its totient is φ = 66446532.

The previous prime is 66638917. The next prime is 66638941. The reversal of 66638921 is 12983666.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 12983666 = 2 ⋅6491833.

It is a cyclic number.

It is not a de Polignac number, because 66638921 - 2² = 66638917 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (66638911) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 95675 + ... + 96368.

It is an arithmetic number, because the mean of its divisors is an integer number (16707828).

Almost surely, 2^66638921 is an apocalyptic number.

It is an amenable number.

66638921 is a deficient number, since it is larger than the sum of its proper divisors (192391).

66638921 is a wasteful number, since it uses less digits than its factorization.

66638921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 192390.

The product of its digits is 93312, while the sum is 41.

The square root of 66638921 is about 8163.2665643111. The cubic root of 66638921 is about 405.4238736497.

The spelling of 66638921 in words is "sixty-six million, six hundred thirty-eight thousand, nine hundred twenty-one".