21211904 has 108 divisors (see below), whose sum is σ = 52428600. Its totient is φ = 8515584.

The previous prime is 21211901. The next prime is 21211909. The reversal of 21211904 is 40911212.

It is not an unprimeable number, because it can be changed into a prime (21211901) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 238292 + ... + 238380.

It is an arithmetic number, because the mean of its divisors is an integer number (485450).

Almost surely, 2^21211904 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 21211904, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26214300).

21211904 is an abundant number, since it is smaller than the sum of its proper divisors (31216696).

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

21211904 is an equidigital number, since it uses as much as digits as its factorization.

21211904 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 138 (or 117 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 20.

The square root of 21211904 is about 4605.6382836693. The cubic root of 21211904 is about 276.8172931827.

The spelling of 21211904 in words is "twenty-one million, two hundred eleven thousand, nine hundred four".