20990531 has 4 divisors (see below), whose sum is σ = 21027864. Its totient is φ = 20953200.

The previous prime is 20990521. The next prime is 20990539. The reversal of 20990531 is 13509902.

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

It is a cyclic number.

It is not a de Polignac number, because 20990531 - 2¹⁸ = 20728387 is a prime.

It is a super-2 number, since 2×20990531² = 881204783323922, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20990494 and 20990503.

It is not an unprimeable number, because it can be changed into a prime (20990539) 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, 17810 + ... + 18951.

It is an arithmetic number, because the mean of its divisors is an integer number (5256966).

Almost surely, 2^20990531 is an apocalyptic number.

20990531 is a deficient number, since it is larger than the sum of its proper divisors (37333).

20990531 is an equidigital number, since it uses as much as digits as its factorization.

20990531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 37332.

The product of its (nonzero) digits is 2430, while the sum is 29.

The square root of 20990531 is about 4581.5424258649. The cubic root of 20990531 is about 275.8509443357.

The spelling of 20990531 in words is "twenty million, nine hundred ninety thousand, five hundred thirty-one".