21217717 has 4 divisors (see below), whose sum is σ = 22465836. Its totient is φ = 19969600.

The previous prime is 21217709. The next prime is 21217739. The reversal of 21217717 is 71771212.

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 9480241 + 11737476 = 3079^2 + 3426^2 .

It is a cyclic number.

It is not a de Polignac number, because 21217717 - 2³ = 21217709 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 (21217747) 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, 624034 + ... + 624067.

It is an arithmetic number, because the mean of its divisors is an integer number (5616459).

Almost surely, 2^21217717 is an apocalyptic number.

It is an amenable number.

21217717 is a deficient number, since it is larger than the sum of its proper divisors (1248119).

21217717 is a wasteful number, since it uses less digits than its factorization.

21217717 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1248118.

The product of its digits is 1372, while the sum is 28.

The square root of 21217717 is about 4606.2693147492. The cubic root of 21217717 is about 276.8425776009.

Adding to 21217717 its reverse (71771212), we get a palindrome (92988929).

The spelling of 21217717 in words is "twenty-one million, two hundred seventeen thousand, seven hundred seventeen".