21790221 has 4 divisors (see below), whose sum is σ = 29053632. Its totient is φ = 14526812.

The previous prime is 21790213. The next prime is 21790247. The reversal of 21790221 is 12209712.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21790221 - 2³ = 21790213 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21790191 and 21790200.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21790201) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3631701 + ... + 3631706.

It is an arithmetic number, because the mean of its divisors is an integer number (7263408).

Almost surely, 2^21790221 is an apocalyptic number.

It is an amenable number.

21790221 is a deficient number, since it is larger than the sum of its proper divisors (7263411).

21790221 is an equidigital number, since it uses as much as digits as its factorization.

21790221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7263410.

The product of its (nonzero) digits is 504, while the sum is 24.

The square root of 21790221 is about 4667.9996786632. Note that the first 3 decimals coincide. The cubic root of 21790221 is about 279.3104674555.

Adding to 21790221 its reverse (12209712), we get a palindrome (33999933).

The spelling of 21790221 in words is "twenty-one million, seven hundred ninety thousand, two hundred twenty-one".