21431820 has 24 divisors (see below), whose sum is σ = 60009264. Its totient is φ = 5715136.

The previous prime is 21431777. The next prime is 21431821. The reversal of 21431820 is 2813412.

It is not an unprimeable number, because it can be changed into a prime (21431821) 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, 178539 + ... + 178658.

It is an arithmetic number, because the mean of its divisors is an integer number (2500386).

Almost surely, 2^21431820 is an apocalyptic number.

21431820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21431820 is an abundant number, since it is smaller than the sum of its proper divisors (38577444).

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

21431820 is a wasteful number, since it uses less digits than its factorization.

21431820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 357209 (or 357207 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 21.

The square root of 21431820 is about 4629.4513713830. The cubic root of 21431820 is about 277.7706474022.

The spelling of 21431820 in words is "twenty-one million, four hundred thirty-one thousand, eight hundred twenty".