21715247 has 2 divisors, whose sum is σ = 21715248. Its totient is φ = 21715246.

The previous prime is 21715231. The next prime is 21715249. The reversal of 21715247 is 74251712.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21715247 - 2⁴ = 21715231 is a prime.

Together with 21715249, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21715249) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10857623 + 10857624.

It is an arithmetic number, because the mean of its divisors is an integer number (10857624).

Almost surely, 2^21715247 is an apocalyptic number.

21715247 is a deficient number, since it is larger than the sum of its proper divisors (1).

21715247 is an equidigital number, since it uses as much as digits as its factorization.

21715247 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3920, while the sum is 29.

The square root of 21715247 is about 4659.9621243096. The cubic root of 21715247 is about 278.9897565215.

Adding to 21715247 its reverse (74251712), we get a palindrome (95966959).

The spelling of 21715247 in words is "twenty-one million, seven hundred fifteen thousand, two hundred forty-seven".