20821861 has 4 divisors (see below), whose sum is σ = 21384652. Its totient is φ = 20259072.

The previous prime is 20821849. The next prime is 20821873. The reversal of 20821861 is 16812802.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (20821849) and next prime (20821873).

It can be written as a sum of positive squares in 2 ways, for example, as 19633761 + 1188100 = 4431^2 + 1090^2 .

It is a cyclic number.

It is not a de Polignac number, because 20821861 - 2⁹ = 20821349 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20821841) 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, 281340 + ... + 281413.

It is an arithmetic number, because the mean of its divisors is an integer number (5346163).

Almost surely, 2^20821861 is an apocalyptic number.

It is an amenable number.

20821861 is a deficient number, since it is larger than the sum of its proper divisors (562791).

20821861 is an equidigital number, since it uses as much as digits as its factorization.

20821861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 562790.

The product of its (nonzero) digits is 1536, while the sum is 28.

The square root of 20821861 is about 4563.0977416663. The cubic root of 20821861 is about 275.1100870539.

The spelling of 20821861 in words is "twenty million, eight hundred twenty-one thousand, eight hundred sixty-one".