20643309 has 16 divisors (see below), whose sum is σ = 30652800. Its totient is φ = 13730688.

The previous prime is 20643269. The next prime is 20643313. The reversal of 20643309 is 90334602.

It is not a de Polignac number, because 20643309 - 2¹⁶ = 20577773 is a prime.

It is a super-2 number, since 2×20643309² = 852292412938962, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20643379) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 21757 + ... + 22685.

It is an arithmetic number, because the mean of its divisors is an integer number (1915800).

Almost surely, 2^20643309 is an apocalyptic number.

It is an amenable number.

20643309 is a deficient number, since it is larger than the sum of its proper divisors (10009491).

20643309 is an equidigital number, since it uses as much as digits as its factorization.

20643309 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1761 (or 1755 counting only the distinct ones).

The product of its (nonzero) digits is 3888, while the sum is 27.

The square root of 20643309 is about 4543.4908385513. The cubic root of 20643309 is about 274.3214521653.

The spelling of 20643309 in words is "twenty million, six hundred forty-three thousand, three hundred nine".