20871821 has 8 divisors (see below), whose sum is σ = 21286584. Its totient is φ = 20459520.

The previous prime is 20871769. The next prime is 20871853. The reversal of 20871821 is 12817802.

It can be written as a sum of positive squares in 4 ways, for example, as 4791721 + 16080100 = 2189^2 + 4010^2 .

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 20871821 - 2⁶ = 20871757 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 (20871881) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 34901 + ... + 35493.

It is an arithmetic number, because the mean of its divisors is an integer number (2660823).

Almost surely, 2^20871821 is an apocalyptic number.

It is an amenable number.

20871821 is a deficient number, since it is larger than the sum of its proper divisors (414763).

20871821 is an equidigital number, since it uses as much as digits as its factorization.

20871821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1231.

The product of its (nonzero) digits is 1792, while the sum is 29.

The square root of 20871821 is about 4568.5688130967. The cubic root of 20871821 is about 275.3299444708.

The spelling of 20871821 in words is "twenty million, eight hundred seventy-one thousand, eight hundred twenty-one".