21715993 has 12 divisors (see below), whose sum is σ = 24756240. Its totient is φ = 18987696.

The previous prime is 21715951. The next prime is 21715997. The reversal of 21715993 is 39951712.

It is a de Polignac number, because none of the positive numbers 2^k-21715993 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21715997) 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, 171 + ... + 6592.

It is an arithmetic number, because the mean of its divisors is an integer number (2063020).

Almost surely, 2^21715993 is an apocalyptic number.

It is an amenable number.

21715993 is a deficient number, since it is larger than the sum of its proper divisors (3040247).

21715993 is a wasteful number, since it uses less digits than its factorization.

21715993 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6808 (or 6795 counting only the distinct ones).

The product of its digits is 17010, while the sum is 37.

The square root of 21715993 is about 4660.0421671912. The cubic root of 21715993 is about 278.9929512657.

The spelling of 21715993 in words is "twenty-one million, seven hundred fifteen thousand, nine hundred ninety-three".