21207717 has 16 divisors (see below), whose sum is σ = 31625280. Its totient is φ = 14045616.

The previous prime is 21207709. The next prime is 21207731. The reversal of 21207717 is 71770212.

It is not a de Polignac number, because 21207717 - 2³ = 21207709 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21207707) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1738 + ... + 6740.

It is an arithmetic number, because the mean of its divisors is an integer number (1976580).

Almost surely, 2^21207717 is an apocalyptic number.

21207717 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

It is an amenable number.

21207717 is a deficient number, since it is larger than the sum of its proper divisors (10417563).

21207717 is a wasteful number, since it uses less digits than its factorization.

21207717 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5169 (or 5163 counting only the distinct ones).

The product of its (nonzero) digits is 1372, while the sum is 27.

The square root of 21207717 is about 4605.1837096906. The cubic root of 21207717 is about 276.7990784061.

Adding to 21207717 its reverse (71770212), we get a palindrome (92977929).

The spelling of 21207717 in words is "twenty-one million, two hundred seven thousand, seven hundred seventeen".