21921993 has 12 divisors (see below), whose sum is σ = 33527988. Its totient is φ = 13754880.

The previous prime is 21921919. The next prime is 21922007. The reversal of 21921993 is 39912912.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 15586704 + 6335289 = 3948^2 + 2517^2 .

It is not a de Polignac number, because 21921993 - 2⁹ = 21921481 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21922993) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 71488 + ... + 71793.

It is an arithmetic number, because the mean of its divisors is an integer number (2793999).

Almost surely, 2^21921993 is an apocalyptic number.

It is an amenable number.

21921993 is a deficient number, since it is larger than the sum of its proper divisors (11605995).

21921993 is a wasteful number, since it uses less digits than its factorization.

21921993 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 143304 (or 143301 counting only the distinct ones).

The product of its digits is 8748, while the sum is 36.

The square root of 21921993 is about 4682.0928013016. The cubic root of 21921993 is about 279.8723610419.

The spelling of 21921993 in words is "twenty-one million, nine hundred twenty-one thousand, nine hundred ninety-three".