21351440 has 80 divisors (see below), whose sum is σ = 57049920. Its totient is φ = 7349760.

The previous prime is 21351433. The next prime is 21351457. The reversal of 21351440 is 4415312.

It is a tau number, because it is divible by the number of its divisors (80).

It is a Harshad number since it is a multiple of its sum of digits (20).

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, 16082 + ... + 17358.

It is an arithmetic number, because the mean of its divisors is an integer number (713124).

Almost surely, 2^21351440 is an apocalyptic number.

21351440 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 21351440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28524960).

21351440 is an abundant number, since it is smaller than the sum of its proper divisors (35698480).

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

21351440 is a wasteful number, since it uses less digits than its factorization.

21351440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1320 (or 1314 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 20.

The square root of 21351440 is about 4620.7618419477. The cubic root of 21351440 is about 277.4229529358.

Adding to 21351440 its reverse (4415312), we get a palindrome (25766752).

The spelling of 21351440 in words is "twenty-one million, three hundred fifty-one thousand, four hundred forty".