20561864 has 8 divisors (see below), whose sum is σ = 38553510. Its totient is φ = 10280928.

The previous prime is 20561843. The next prime is 20561867. The reversal of 20561864 is 46816502.

It can be written as a sum of positive squares in only one way, i.e., 16728100 + 3833764 = 4090^2 + 1958^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is a self number, because there is not a number n which added to its sum of digits gives 20561864.

It is not an unprimeable number, because it can be changed into a prime (20561867) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1285109 + ... + 1285124.

Almost surely, 2^20561864 is an apocalyptic number.

It is an amenable number.

20561864 is a deficient number, since it is larger than the sum of its proper divisors (17991646).

20561864 is a wasteful number, since it uses less digits than its factorization.

20561864 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2570239 (or 2570235 counting only the distinct ones).

The product of its (nonzero) digits is 11520, while the sum is 32.

The square root of 20561864 is about 4534.5191586319. The cubic root of 20561864 is about 273.9602123128.

The spelling of 20561864 in words is "twenty million, five hundred sixty-one thousand, eight hundred sixty-four".