21380240 has 80 divisors (see below), whose sum is σ = 57698688. Its totient is φ = 7216128.

The previous prime is 21380207. The next prime is 21380257. The reversal of 21380240 is 4208312.

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

It is a super-2 number, since 2×21380240² = 914229324915200, which contains 22 as substring.

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, 40619 + ... + 41141.

Almost surely, 2^21380240 is an apocalyptic number.

21380240 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 21380240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28849344).

21380240 is an abundant number, since it is smaller than the sum of its proper divisors (36318448).

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

21380240 is a wasteful number, since it uses less digits than its factorization.

21380240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 616 (or 610 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 20.

The square root of 21380240 is about 4623.8771609981. The cubic root of 21380240 is about 277.5476313553.

Adding to 21380240 its reverse (4208312), we get a palindrome (25588552).

The spelling of 21380240 in words is "twenty-one million, three hundred eighty thousand, two hundred forty".