21715901 has 4 divisors (see below), whose sum is σ = 21826332. Its totient is φ = 21605472.

The previous prime is 21715891. The next prime is 21715907. The reversal of 21715901 is 10951712.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 21576025 + 139876 = 4645^2 + 374^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21715901 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21715907) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 54920 + ... + 55313.

It is an arithmetic number, because the mean of its divisors is an integer number (5456583).

Almost surely, 2^21715901 is an apocalyptic number.

It is an amenable number.

21715901 is a deficient number, since it is larger than the sum of its proper divisors (110431).

21715901 is a wasteful number, since it uses less digits than its factorization.

21715901 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 110430.

The product of its (nonzero) digits is 630, while the sum is 26.

The square root of 21715901 is about 4660.0322960254. The cubic root of 21715901 is about 278.9925572797.

The spelling of 21715901 in words is "twenty-one million, seven hundred fifteen thousand, nine hundred one".