21789217 has 4 divisors (see below), whose sum is σ = 21800596. Its totient is φ = 21777840.

The previous prime is 21789203. The next prime is 21789233. The reversal of 21789217 is 71298712.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 17943696 + 3845521 = 4236^2 + 1961^2 .

It is a cyclic number.

It is not a de Polignac number, because 21789217 - 2¹¹ = 21787169 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21789617) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2034 + ... + 6907.

It is an arithmetic number, because the mean of its divisors is an integer number (5450149).

Almost surely, 2^21789217 is an apocalyptic number.

It is an amenable number.

21789217 is a deficient number, since it is larger than the sum of its proper divisors (11379).

21789217 is an equidigital number, since it uses as much as digits as its factorization.

21789217 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11378.

The product of its digits is 14112, while the sum is 37.

The square root of 21789217 is about 4667.8921367144. The cubic root of 21789217 is about 279.3061775798.

The spelling of 21789217 in words is "twenty-one million, seven hundred eighty-nine thousand, two hundred seventeen".