20643557 has 8 divisors (see below), whose sum is σ = 23705760. Its totient is φ = 17778960.

The previous prime is 20643547. The next prime is 20643587. The reversal of 20643557 is 75534602.

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

It is a cyclic number.

It is not a de Polignac number, because 20643557 - 2¹⁶ = 20578021 is a prime.

It is a super-2 number, since 2×20643557² = 852312891224498, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20643517) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 49178 + ... + 49595.

It is an arithmetic number, because the mean of its divisors is an integer number (2963220).

Almost surely, 2^20643557 is an apocalyptic number.

It is an amenable number.

20643557 is a deficient number, since it is larger than the sum of its proper divisors (3062203).

20643557 is a wasteful number, since it uses less digits than its factorization.

20643557 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 98803.

The product of its (nonzero) digits is 25200, while the sum is 32.

The square root of 20643557 is about 4543.5181302599. The cubic root of 20643557 is about 274.3225506883.

Subtracting from 20643557 its sum of digits (32), we obtain a triangular number (20643525 = T₆₄₂₅).

The spelling of 20643557 in words is "twenty million, six hundred forty-three thousand, five hundred fifty-seven".