21604266 has 32 divisors (see below), whose sum is σ = 48830400. Its totient is φ = 7078320.

The previous prime is 21604249. The next prime is 21604267. The reversal of 21604266 is 66240612.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21604267) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 205 + ... + 6576.

It is an arithmetic number, because the mean of its divisors is an integer number (1525950).

Almost surely, 2^21604266 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21604266, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24415200).

21604266 is an abundant number, since it is smaller than the sum of its proper divisors (27226134).

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

21604266 is a wasteful number, since it uses less digits than its factorization.

21604266 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6851 (or 6845 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 27.

The square root of 21604266 is about 4648.0389413171. The cubic root of 21604266 is about 278.5136630858.

Adding to 21604266 its reverse (66240612), we get a palindrome (87844878).

The spelling of 21604266 in words is "twenty-one million, six hundred four thousand, two hundred sixty-six".