21306240 has 192 divisors, whose sum is σ = 76854960. Its totient is φ = 5640192.

The previous prime is 21306227. The next prime is 21306247. The reversal of 21306240 is 4260312.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (192).

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 (21306247) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 155452 + ... + 155588.

Almost surely, 2^21306240 is an apocalyptic number.

21306240 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 21306240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38427480).

21306240 is an abundant number, since it is smaller than the sum of its proper divisors (55548720).

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

21306240 is an equidigital number, since it uses as much as digits as its factorization.

21306240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 171 (or 147 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 18.

The square root of 21306240 is about 4615.8682823495. The cubic root of 21306240 is about 277.2270508261.

Adding to 21306240 its reverse (4260312), we get a palindrome (25566552).

The spelling of 21306240 in words is "twenty-one million, three hundred six thousand, two hundred forty".