21304440 has 192 divisors, whose sum is σ = 75479040. Its totient is φ = 5195520.

The previous prime is 21304427. The next prime is 21304441. The reversal of 21304440 is 4440312.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21304441) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 256639 + ... + 256721.

It is an arithmetic number, because the mean of its divisors is an integer number (393120).

Almost surely, 2^21304440 is an apocalyptic number.

21304440 is a gapful number since it is divisible by the number (20) 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 21304440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37739520).

21304440 is an abundant number, since it is smaller than the sum of its proper divisors (54174600).

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

21304440 is a wasteful number, since it uses less digits than its factorization.

21304440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 154 (or 147 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 18.

The square root of 21304440 is about 4615.6732986640. The cubic root of 21304440 is about 277.2192436807.

Adding to 21304440 its reverse (4440312), we get a palindrome (25744752).

The spelling of 21304440 in words is "twenty-one million, three hundred four thousand, four hundred forty".