20640657 has 8 divisors (see below), whose sum is σ = 27645184. Its totient is φ = 13698288.

The previous prime is 20640647. The next prime is 20640667. The reversal of 20640657 is 75604602.

It is an interprime number because it is at equal distance from previous prime (20640647) and next prime (20640667).

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

It is not a de Polignac number, because 20640657 - 2⁸ = 20640401 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20640617) 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, 14758 + ... + 16095.

It is an arithmetic number, because the mean of its divisors is an integer number (3455648).

Almost surely, 2^20640657 is an apocalyptic number.

It is an amenable number.

20640657 is a deficient number, since it is larger than the sum of its proper divisors (7004527).

20640657 is a wasteful number, since it uses less digits than its factorization.

20640657 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 31079.

The product of its (nonzero) digits is 10080, while the sum is 30.

The square root of 20640657 is about 4543.1989830955. The cubic root of 20640657 is about 274.3097045066.

The spelling of 20640657 in words is "twenty million, six hundred forty thousand, six hundred fifty-seven".