20990831 has 2 divisors, whose sum is σ = 20990832. Its totient is φ = 20990830.

The previous prime is 20990821. The next prime is 20990833. The reversal of 20990831 is 13809902.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 20990831 - 2¹⁰ = 20989807 is a prime.

It is a super-2 number, since 2×20990831² = 881229972141122, which contains 22 as substring.

Together with 20990833, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20990833) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10495415 + 10495416.

It is an arithmetic number, because the mean of its divisors is an integer number (10495416).

Almost surely, 2^20990831 is an apocalyptic number.

20990831 is a deficient number, since it is larger than the sum of its proper divisors (1).

20990831 is an equidigital number, since it uses as much as digits as its factorization.

20990831 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3888, while the sum is 32.

The square root of 20990831 is about 4581.5751658136. The cubic root of 20990831 is about 275.8522584979.

The spelling of 20990831 in words is "twenty million, nine hundred ninety thousand, eight hundred thirty-one".