21171920 has 120 divisors (see below), whose sum is σ = 62594208. Its totient is φ = 6585600.

The previous prime is 21171911. The next prime is 21171929. The reversal of 21171920 is 2917112.

It is an interprime number because it is at equal distance from previous prime (21171911) and next prime (21171929).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21171929) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 42875 + ... + 43365.

Almost surely, 2^21171920 is an apocalyptic number.

21171920 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 21171920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31297104).

21171920 is an abundant number, since it is smaller than the sum of its proper divisors (41422288).

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

21171920 is a wasteful number, since it uses less digits than its factorization.

21171920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 529 (or 516 counting only the distinct ones).

The product of its (nonzero) digits is 252, while the sum is 23.

The square root of 21171920 is about 4601.2954697563. The cubic root of 21171920 is about 276.6432521595.

The spelling of 21171920 in words is "twenty-one million, one hundred seventy-one thousand, nine hundred twenty".