21715999 has 2 divisors, whose sum is σ = 21716000. Its totient is φ = 21715998.

The previous prime is 21715997. The next prime is 21716017. The reversal of 21715999 is 99951712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21715999 - 2¹ = 21715997 is a prime.

It is a super-2 number, since 2×21715999² = 943169225136002, which contains 22 as substring.

Together with 21715997, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21715997) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10857999 + 10858000.

It is an arithmetic number, because the mean of its divisors is an integer number (10858000).

Almost surely, 2^21715999 is an apocalyptic number.

21715999 is a deficient number, since it is larger than the sum of its proper divisors (1).

21715999 is an equidigital number, since it uses as much as digits as its factorization.

21715999 is an evil number, because the sum of its binary digits is even.

The product of its digits is 51030, while the sum is 43.

The square root of 21715999 is about 4660.0428109621. The cubic root of 21715999 is about 278.9929769604.

The spelling of 21715999 in words is "twenty-one million, seven hundred fifteen thousand, nine hundred ninety-nine".