2021578561 has 4 divisors (see below), whose sum is σ = 2049271492. Its totient is φ = 1993885632.

The previous prime is 2021578459. The next prime is 2021578567. The reversal of 2021578561 is 1658751202.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1658751202 = 2 ⋅829375601.

It can be written as a sum of positive squares in 2 ways, for example, as 586608400 + 1434970161 = 24220^2 + 37881^2 .

It is a cyclic number.

It is not a de Polignac number, because 2021578561 - 2¹⁷ = 2021447489 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 2021578561.

It is not an unprimeable number, because it can be changed into a prime (2021578567) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 13846356 + ... + 13846501.

It is an arithmetic number, because the mean of its divisors is an integer number (512317873).

Almost surely, 2^2021578561 is an apocalyptic number.

It is an amenable number.

2021578561 is a deficient number, since it is larger than the sum of its proper divisors (27692931).

2021578561 is an equidigital number, since it uses as much as digits as its factorization.

2021578561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27692930.

The product of its (nonzero) digits is 33600, while the sum is 37.

The square root of 2021578561 is about 44961.9679395820. The cubic root of 2021578561 is about 1264.4360645704.

The spelling of 2021578561 in words is "two billion, twenty-one million, five hundred seventy-eight thousand, five hundred sixty-one".