21768993 has 20 divisors (see below), whose sum is σ = 34434180. Its totient is φ = 13658112.

The previous prime is 21768961. The next prime is 21768997. The reversal of 21768993 is 39986712.

It can be written as a sum of positive squares in 2 ways, for example, as 7683984 + 14085009 = 2772^2 + 3753^2 .

It is not a de Polignac number, because 21768993 - 2⁵ = 21768961 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21768997) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 6528 + ... + 9281.

It is an arithmetic number, because the mean of its divisors is an integer number (1721709).

Almost surely, 2^21768993 is an apocalyptic number.

It is an amenable number.

21768993 is a deficient number, since it is larger than the sum of its proper divisors (12665187).

21768993 is a wasteful number, since it uses less digits than its factorization.

21768993 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15838 (or 15829 counting only the distinct ones).

The product of its digits is 163296, while the sum is 45.

The square root of 21768993 is about 4665.7253455385. The cubic root of 21768993 is about 279.2197367090.

The spelling of 21768993 in words is "twenty-one million, seven hundred sixty-eight thousand, nine hundred ninety-three".