21989993 has 4 divisors (see below), whose sum is σ = 23283540. Its totient is φ = 20696448.

The previous prime is 21989983. The next prime is 21989999. The reversal of 21989993 is 39998912.

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 18593344 + 3396649 = 4312^2 + 1843^2 .

It is a cyclic number.

It is not a de Polignac number, because 21989993 - 2¹⁰ = 21988969 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21989999) 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 3 ways as a sum of consecutive naturals, for example, 646748 + ... + 646781.

It is an arithmetic number, because the mean of its divisors is an integer number (5820885).

Almost surely, 2^21989993 is an apocalyptic number.

It is an amenable number.

21989993 is a deficient number, since it is larger than the sum of its proper divisors (1293547).

21989993 is a wasteful number, since it uses less digits than its factorization.

21989993 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1293546.

The product of its digits is 314928, while the sum is 50.

The square root of 21989993 is about 4689.3488887051. The cubic root of 21989993 is about 280.1614417623.

The spelling of 21989993 in words is "twenty-one million, nine hundred eighty-nine thousand, nine hundred ninety-three".