21345440 has 48 divisors (see below), whose sum is σ = 51166080. Its totient is φ = 8413440.

The previous prime is 21345431. The next prime is 21345451. The reversal of 21345440 is 4454312.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10421 + ... + 12299.

It is an arithmetic number, because the mean of its divisors is an integer number (1065960).

Almost surely, 2^21345440 is an apocalyptic number.

21345440 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 21345440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25583040).

21345440 is an abundant number, since it is smaller than the sum of its proper divisors (29820640).

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

21345440 is a wasteful number, since it uses less digits than its factorization.

21345440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1965 (or 1957 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 23.

The square root of 21345440 is about 4620.1125527415. The cubic root of 21345440 is about 277.3969641553.

Adding to 21345440 its reverse (4454312), we get a palindrome (25799752).

The spelling of 21345440 in words is "twenty-one million, three hundred forty-five thousand, four hundred forty".