21391104 has 144 divisors (see below), whose sum is σ = 68285952. Its totient is φ = 5812224.

The previous prime is 21391091. The next prime is 21391129. The reversal of 21391104 is 40119312.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 123562 + ... + 123734.

It is an arithmetic number, because the mean of its divisors is an integer number (474208).

Almost surely, 2^21391104 is an apocalyptic number.

21391104 is a gapful number since it is divisible by the number (24) 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 21391104, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34142976).

21391104 is an abundant number, since it is smaller than the sum of its proper divisors (46894848).

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

21391104 is a wasteful number, since it uses less digits than its factorization.

21391104 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 222 (or 208 counting only the distinct ones).

The product of its (nonzero) digits is 216, while the sum is 21.

The square root of 21391104 is about 4625.0517834939. The cubic root of 21391104 is about 277.5946337415.

The spelling of 21391104 in words is "twenty-one million, three hundred ninety-one thousand, one hundred four".