21993387 has 8 divisors (see below), whose sum is σ = 31580304. Its totient is φ = 13534368.

The previous prime is 21993347. The next prime is 21993401. The reversal of 21993387 is 78339912.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21993387 - 2⁷ = 21993259 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21993347) 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, 281928 + ... + 282005.

It is an arithmetic number, because the mean of its divisors is an integer number (3947538).

Almost surely, 2^21993387 is an apocalyptic number.

21993387 is a deficient number, since it is larger than the sum of its proper divisors (9586917).

21993387 is a wasteful number, since it uses less digits than its factorization.

21993387 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 563949.

The product of its digits is 81648, while the sum is 42.

The square root of 21993387 is about 4689.7107586716. The cubic root of 21993387 is about 280.1758546670.

The spelling of 21993387 in words is "twenty-one million, nine hundred ninety-three thousand, three hundred eighty-seven".