21788221 has 8 divisors (see below), whose sum is σ = 26816384. Its totient is φ = 17238960.

The previous prime is 21788201. The next prime is 21788233. The reversal of 21788221 is 12288712.

21788221 = T₆₄₆ + T₆₄₇ + ... + T₇₃₆.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21788221 - 2⁷ = 21788093 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21788201) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 119625 + ... + 119806.

It is an arithmetic number, because the mean of its divisors is an integer number (3352048).

Almost surely, 2^21788221 is an apocalyptic number.

It is an amenable number.

21788221 is a deficient number, since it is larger than the sum of its proper divisors (5028163).

21788221 is a wasteful number, since it uses less digits than its factorization.

21788221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 239451.

The product of its digits is 3584, while the sum is 31.

The square root of 21788221 is about 4667.7854492254. The cubic root of 21788221 is about 279.3019217562.

The spelling of 21788221 in words is "twenty-one million, seven hundred eighty-eight thousand, two hundred twenty-one".