21123791 has 8 divisors (see below), whose sum is σ = 23061360. Its totient is φ = 19230912.

The previous prime is 21123779. The next prime is 21123841. The reversal of 21123791 is 19732112.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21123791 - 2¹⁴ = 21107407 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21123791.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21123701) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10181 + ... + 12078.

It is an arithmetic number, because the mean of its divisors is an integer number (2882670).

Almost surely, 2^21123791 is an apocalyptic number.

21123791 is a deficient number, since it is larger than the sum of its proper divisors (1937569).

21123791 is a wasteful number, since it uses less digits than its factorization.

21123791 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22345.

The product of its digits is 756, while the sum is 26.

The square root of 21123791 is about 4596.0625539694. The cubic root of 21123791 is about 276.4334669827.

The spelling of 21123791 in words is "twenty-one million, one hundred twenty-three thousand, seven hundred ninety-one".