21392640 has 144 divisors (see below), whose sum is σ = 76036800. Its totient is φ = 5695488.

The previous prime is 21392621. The next prime is 21392641. The reversal of 21392640 is 4629312.

21392640 is a `hidden beast` number, since 2 + 13 + 9 + 2 + 640 = 666.

It is a tau number, because it is divible by the number of its divisors (144).

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21392641) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 34251 + ... + 34869.

Almost surely, 2^21392640 is an apocalyptic number.

21392640 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 21392640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38018400).

21392640 is an abundant number, since it is smaller than the sum of its proper divisors (54644160).

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

21392640 is an equidigital number, since it uses as much as digits as its factorization.

21392640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 649 (or 629 counting only the distinct ones).

The product of its (nonzero) digits is 2592, while the sum is 27.

The square root of 21392640 is about 4625.2178327080. The cubic root of 21392640 is about 277.6012778609.

The spelling of 21392640 in words is "twenty-one million, three hundred ninety-two thousand, six hundred forty".