20921868 has 72 divisors (see below), whose sum is σ = 59658480. Its totient is φ = 6336000.

The previous prime is 20921867. The next prime is 20921897. The reversal of 20921868 is 86812902.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is not an unprimeable number, because it can be changed into a prime (20921867) 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, 12268 + ... + 13868.

It is an arithmetic number, because the mean of its divisors is an integer number (828590).

Almost surely, 2^20921868 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 20921868, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29829240).

20921868 is an abundant number, since it is smaller than the sum of its proper divisors (38736612).

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

20921868 is a wasteful number, since it uses less digits than its factorization.

20921868 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1636 (or 1617 counting only the distinct ones).

The product of its (nonzero) digits is 13824, while the sum is 36.

The square root of 20921868 is about 4574.0428506957. The cubic root of 20921868 is about 275.5498332675.

The spelling of 20921868 in words is "twenty million, nine hundred twenty-one thousand, eight hundred sixty-eight".