21281820 has 48 divisors (see below), whose sum is σ = 68103168. Its totient is φ = 4864320.

The previous prime is 21281797. The next prime is 21281891. The reversal of 21281820 is 2818212.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 24916 + ... + 25755.

It is an arithmetic number, because the mean of its divisors is an integer number (1418816).

Almost surely, 2^21281820 is an apocalyptic number.

21281820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21281820 is an abundant number, since it is smaller than the sum of its proper divisors (46821348).

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

21281820 is a wasteful number, since it uses less digits than its factorization.

21281820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 50690 (or 50688 counting only the distinct ones).

The product of its (nonzero) digits is 512, while the sum is 24.

The square root of 21281820 is about 4613.2223011687. Note that the first 3 decimals coincide. The cubic root of 21281820 is about 277.1210963789.

The spelling of 21281820 in words is "twenty-one million, two hundred eighty-one thousand, eight hundred twenty".