21393988 has 36 divisors (see below), whose sum is σ = 47516112. Its totient is φ = 8334480.

The previous prime is 21393961. The next prime is 21393989. The reversal of 21393988 is 88939312.

It is a happy number.

It is a Smith number, since the sum of its digits (43) coincides with the sum of the digits of its prime factors.

It is not an unprimeable number, because it can be changed into a prime (21393989) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2806 + ... + 7117.

It is an arithmetic number, because the mean of its divisors is an integer number (1319892).

Almost surely, 2^21393988 is an apocalyptic number.

21393988 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

21393988 is an abundant number, since it is smaller than the sum of its proper divisors (26122124).

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

21393988 is a wasteful number, since it uses less digits than its factorization.

21393988 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9952 (or 9943 counting only the distinct ones).

The product of its digits is 93312, while the sum is 43.

The square root of 21393988 is about 4625.3635532788. The cubic root of 21393988 is about 277.6071085059.

The spelling of 21393988 in words is "twenty-one million, three hundred ninety-three thousand, nine hundred eighty-eight".