20643865 has 16 divisors (see below), whose sum is σ = 28615680. Its totient is φ = 14129920.

The previous prime is 20643851. The next prime is 20643893. The reversal of 20643865 is 56834602.

It is a happy number.

It is not a de Polignac number, because 20643865 - 2⁹ = 20643353 is a prime.

It is a super-3 number, since 3×20643865³ (a number of 23 digits) contains 333 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 20643865.

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, 10105 + ... + 11974.

It is an arithmetic number, because the mean of its divisors is an integer number (1788480).

Almost surely, 2^20643865 is an apocalyptic number.

It is an amenable number.

20643865 is a deficient number, since it is larger than the sum of its proper divisors (7971815).

20643865 is a wasteful number, since it uses less digits than its factorization.

20643865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22112.

The product of its (nonzero) digits is 34560, while the sum is 34.

The square root of 20643865 is about 4543.5520245728. The cubic root of 20643865 is about 274.3239149707.

It can be divided in two parts, 2064 and 3865, that added together give a square (5929 = 77²).

The spelling of 20643865 in words is "twenty million, six hundred forty-three thousand, eight hundred sixty-five".