21161920 has 56 divisors (see below), whose sum is σ = 54278784. Its totient is φ = 7812096.

The previous prime is 21161911. The next prime is 21161927. The reversal of 21161920 is 2916112.

It is a junction number, because it is equal to n+sod(n) for n = 21161891 and 21161900.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21161927) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 1617 + ... + 6703.

It is an arithmetic number, because the mean of its divisors is an integer number (969264).

Almost surely, 2^21161920 is an apocalyptic number.

21161920 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 21161920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27139392).

21161920 is an abundant number, since it is smaller than the sum of its proper divisors (33116864).

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

21161920 is a wasteful number, since it uses less digits than its factorization.

21161920 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5117 (or 5107 counting only the distinct ones).

The product of its (nonzero) digits is 216, while the sum is 22.

The square root of 21161920 is about 4600.2086909183. The cubic root of 21161920 is about 276.5996902438.

The spelling of 21161920 in words is "twenty-one million, one hundred sixty-one thousand, nine hundred twenty".