21866221 has 4 divisors (see below), whose sum is σ = 23548252. Its totient is φ = 20184192.

The previous prime is 21866219. The next prime is 21866239. The reversal of 21866221 is 12266812.

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 14364100 + 7502121 = 3790^2 + 2739^2 .

It is a cyclic number.

It is not a de Polignac number, because 21866221 - 2¹ = 21866219 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21866221.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21866021) 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, 840996 + ... + 841021.

It is an arithmetic number, because the mean of its divisors is an integer number (5887063).

Almost surely, 2^21866221 is an apocalyptic number.

It is an amenable number.

21866221 is a deficient number, since it is larger than the sum of its proper divisors (1682031).

21866221 is a wasteful number, since it uses less digits than its factorization.

21866221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1682030.

The product of its digits is 2304, while the sum is 28.

The square root of 21866221 is about 4676.1331247089. The cubic root of 21866221 is about 279.6348172944.

The spelling of 21866221 in words is "twenty-one million, eight hundred sixty-six thousand, two hundred twenty-one".