21221999 has 4 divisors (see below), whose sum is σ = 21266064. Its totient is φ = 21177936.

The previous prime is 21221953. The next prime is 21222013. The reversal of 21221999 is 99912212.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21221999 - 2⁸ = 21221743 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21221909) 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, 21302 + ... + 22275.

It is an arithmetic number, because the mean of its divisors is an integer number (5316516).

Almost surely, 2^21221999 is an apocalyptic number.

21221999 is a deficient number, since it is larger than the sum of its proper divisors (44065).

21221999 is an equidigital number, since it uses as much as digits as its factorization.

21221999 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 44064.

The product of its digits is 5832, while the sum is 35.

The square root of 21221999 is about 4606.7340926083. The cubic root of 21221999 is about 276.8611997769.

The spelling of 21221999 in words is "twenty-one million, two hundred twenty-one thousand, nine hundred ninety-nine".