21981920 has 24 divisors (see below), whose sum is σ = 51932664. Its totient is φ = 8792704.

The previous prime is 21981893. The next prime is 21981923. The reversal of 21981920 is 2918912.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (32).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21981923) 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, 68534 + ... + 68853.

It is an arithmetic number, because the mean of its divisors is an integer number (2163861).

Almost surely, 2^21981920 is an apocalyptic number.

21981920 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21981920 is an abundant number, since it is smaller than the sum of its proper divisors (29950744).

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

21981920 is a wasteful number, since it uses less digits than its factorization.

21981920 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 137402 (or 137394 counting only the distinct ones).

The product of its (nonzero) digits is 2592, while the sum is 32.

The square root of 21981920 is about 4688.4880292052. The cubic root of 21981920 is about 280.1271531330.

The spelling of 21981920 in words is "twenty-one million, nine hundred eighty-one thousand, nine hundred twenty".