21358991 has 8 divisors (see below), whose sum is σ = 21945168. Its totient is φ = 20776000.

The previous prime is 21358979. The next prime is 21358999. The reversal of 21358991 is 19985312.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21358991 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21358999) 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, 19601 + ... + 20661.

It is an arithmetic number, because the mean of its divisors is an integer number (2743146).

Almost surely, 2^21358991 is an apocalyptic number.

21358991 is a deficient number, since it is larger than the sum of its proper divisors (586177).

21358991 is a wasteful number, since it uses less digits than its factorization.

21358991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1593.

The product of its digits is 19440, while the sum is 38.

The square root of 21358991 is about 4621.5788427766. The cubic root of 21358991 is about 277.4556528976.

The spelling of 21358991 in words is "twenty-one million, three hundred fifty-eight thousand, nine hundred ninety-one".