21388940 has 24 divisors (see below), whose sum is σ = 45008880. Its totient is φ = 8538048.

The previous prime is 21388897. The next prime is 21388943. The reversal of 21388940 is 4988312.

It is a happy number.

It is a zygodrome in base 9.

It is a self number, because there is not a number n which added to its sum of digits gives 21388940.

It is not an unprimeable number, because it can be changed into a prime (21388943) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 13931 + ... + 15389.

It is an arithmetic number, because the mean of its divisors is an integer number (1875370).

Almost surely, 2^21388940 is an apocalyptic number.

21388940 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21388940 is an abundant number, since it is smaller than the sum of its proper divisors (23619940).

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

21388940 is a wasteful number, since it uses less digits than its factorization.

21388940 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2201 (or 2199 counting only the distinct ones).

The product of its (nonzero) digits is 13824, while the sum is 35.

The square root of 21388940 is about 4624.8178342503. The cubic root of 21388940 is about 277.5852726063.

The spelling of 21388940 in words is "twenty-one million, three hundred eighty-eight thousand, nine hundred forty".