20391880 has 16 divisors (see below), whose sum is σ = 45881820. Its totient is φ = 8156736.

The previous prime is 20391851. The next prime is 20391887. The reversal of 20391880 is 8819302.

It can be written as a sum of positive squares in 2 ways, for example, as 18369796 + 2022084 = 4286^2 + 1422^2 .

It is not an unprimeable number, because it can be changed into a prime (20391887) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 254859 + ... + 254938.

Almost surely, 2^20391880 is an apocalyptic number.

20391880 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20391880 is an abundant number, since it is smaller than the sum of its proper divisors (25489940).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

20391880 is a wasteful number, since it uses less digits than its factorization.

20391880 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 509808 (or 509804 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 31.

The square root of 20391880 is about 4515.7369276786. The cubic root of 20391880 is about 273.2031834606.

The spelling of 20391880 in words is "twenty million, three hundred ninety-one thousand, eight hundred eighty".