21909920 has 48 divisors (see below), whose sum is σ = 53175528. Its totient is φ = 8524800.

The previous prime is 21909917. The next prime is 21909941. The reversal of 21909920 is 2990912.

It can be written as a sum of positive squares in 4 ways, for example, as 20178064 + 1731856 = 4492^2 + 1316^2 .

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

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4070 + ... + 7770.

Almost surely, 2^21909920 is an apocalyptic number.

21909920 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21909920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26587764).

21909920 is an abundant number, since it is smaller than the sum of its proper divisors (31265608).

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

21909920 is a wasteful number, since it uses less digits than its factorization.

21909920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3753 (or 3745 counting only the distinct ones).

The product of its (nonzero) digits is 2916, while the sum is 32.

The square root of 21909920 is about 4680.8033498535. The cubic root of 21909920 is about 279.8209739944.

The spelling of 21909920 in words is "twenty-one million, nine hundred nine thousand, nine hundred twenty".