21004456 has 32 divisors (see below), whose sum is σ = 44131680. Its totient is φ = 9288000.

The previous prime is 21004447. The next prime is 21004457. The reversal of 21004456 is 65440012.

It is a Harshad number since it is a multiple of its sum of digits (22).

It is not an unprimeable number, because it can be changed into a prime (21004457) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 31 + ... + 6481.

It is an arithmetic number, because the mean of its divisors is an integer number (1379115).

Almost surely, 2^21004456 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 21004456, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22065840).

21004456 is an abundant number, since it is smaller than the sum of its proper divisors (23127224).

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

21004456 is a wasteful number, since it uses less digits than its factorization.

21004456 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6505 (or 6501 counting only the distinct ones).

The product of its (nonzero) digits is 960, while the sum is 22.

The square root of 21004456 is about 4583.0618586268. The cubic root of 21004456 is about 275.9119301725.

Adding to 21004456 its reverse (65440012), we get a palindrome (86444468).

Subtracting 21004456 from its reverse (65440012), we obtain a square (44435556 = 6666²).

It can be divided in two parts, 2100 and 4456, that added together give a palindrome (6556).

The spelling of 21004456 in words is "twenty-one million, four thousand, four hundred fifty-six".