21380640 has 48 divisors (see below), whose sum is σ = 67350528. Its totient is φ = 5701376.

The previous prime is 21380621. The next prime is 21380657. The reversal of 21380640 is 4608312.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (48).

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a self number, because there is not a number n which added to its sum of digits gives 21380640.

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, 21792 + ... + 22751.

It is an arithmetic number, because the mean of its divisors is an integer number (1403136).

Almost surely, 2^21380640 is an apocalyptic number.

21380640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21380640 is an abundant number, since it is smaller than the sum of its proper divisors (45969888).

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

21380640 is a wasteful number, since it uses less digits than its factorization.

21380640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 44561 (or 44553 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 24.

The square root of 21380640 is about 4623.9204145400. The cubic root of 21380640 is about 277.5493622115.

Adding to 21380640 its reverse (4608312), we get a palindrome (25988952).

The spelling of 21380640 in words is "twenty-one million, three hundred eighty thousand, six hundred forty".