21931221 has 16 divisors (see below), whose sum is σ = 32578560. Its totient is φ = 13030080.

The previous prime is 21931219. The next prime is 21931223. The reversal of 21931221 is 12213912.

It is an interprime number because it is at equal distance from previous prime (21931219) and next prime (21931223).

It is not a de Polignac number, because 21931221 - 2¹ = 21931219 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21931223) 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 15 ways as a sum of consecutive naturals, for example, 8565 + ... + 10826.

It is an arithmetic number, because the mean of its divisors is an integer number (2036160).

Almost surely, 2^21931221 is an apocalyptic number.

It is an amenable number.

21931221 is a deficient number, since it is larger than the sum of its proper divisors (10647339).

21931221 is a wasteful number, since it uses less digits than its factorization.

21931221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19436.

The product of its digits is 216, while the sum is 21.

The square root of 21931221 is about 4683.0781543767. The cubic root of 21931221 is about 279.9116260218.

The spelling of 21931221 in words is "twenty-one million, nine hundred thirty-one thousand, two hundred twenty-one".