21768217 has 4 divisors (see below), whose sum is σ = 21808996. Its totient is φ = 21727440.

The previous prime is 21768203. The next prime is 21768221. The reversal of 21768217 is 71286712.

It is a happy number.

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 12702096 + 9066121 = 3564^2 + 3011^2 .

It is a cyclic number.

It is not a de Polignac number, because 21768217 - 2²³ = 13379609 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21768917) 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, 19578 + ... + 20659.

It is an arithmetic number, because the mean of its divisors is an integer number (5452249).

Almost surely, 2^21768217 is an apocalyptic number.

It is an amenable number.

21768217 is a deficient number, since it is larger than the sum of its proper divisors (40779).

21768217 is an equidigital number, since it uses as much as digits as its factorization.

21768217 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40778.

The product of its digits is 9408, while the sum is 34.

The square root of 21768217 is about 4665.6421851659. The cubic root of 21768217 is about 279.2164188846.

The spelling of 21768217 in words is "twenty-one million, seven hundred sixty-eight thousand, two hundred seventeen".