20643665 has 16 divisors (see below), whose sum is σ = 28425600. Its totient is φ = 14098560.

The previous prime is 20643643. The next prime is 20643683. The reversal of 20643665 is 56634602.

It is not a de Polignac number, because 20643665 - 2¹² = 20639569 is a prime.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 8786 + ... + 10884.

It is an arithmetic number, because the mean of its divisors is an integer number (1776600).

Almost surely, 2^20643665 is an apocalyptic number.

It is an amenable number.

20643665 is a deficient number, since it is larger than the sum of its proper divisors (7781935).

20643665 is a wasteful number, since it uses less digits than its factorization.

20643665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2392.

The product of its (nonzero) digits is 25920, while the sum is 32.

The square root of 20643665 is about 4543.5300153075. The cubic root of 20643665 is about 274.3230290746.

The spelling of 20643665 in words is "twenty million, six hundred forty-three thousand, six hundred sixty-five".