20643813 has 6 divisors (see below), whose sum is σ = 29818854. Its totient is φ = 13762536.

The previous prime is 20643809. The next prime is 20643851. The reversal of 20643813 is 31834602.

It is a happy number.

20643813 is a `hidden beast` number, since 2 + 0 + 643 + 8 + 13 = 666.

It can be written as a sum of positive squares in only one way, i.e., 18948609 + 1695204 = 4353^2 + 1302^2 .

It is not a de Polignac number, because 20643813 - 2² = 20643809 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20643893) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1146870 + ... + 1146887.

It is an arithmetic number, because the mean of its divisors is an integer number (4969809).

Almost surely, 2^20643813 is an apocalyptic number.

It is an amenable number.

20643813 is a deficient number, since it is larger than the sum of its proper divisors (9175041).

20643813 is a wasteful number, since it uses less digits than its factorization.

20643813 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2293763 (or 2293760 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 27.

The square root of 20643813 is about 4543.5463021741. The cubic root of 20643813 is about 274.3236846383.

The spelling of 20643813 in words is "twenty million, six hundred forty-three thousand, eight hundred thirteen".