21991359 has 8 divisors (see below), whose sum is σ = 31577392. Its totient is φ = 13533120.

The previous prime is 21991349. The next prime is 21991397. The reversal of 21991359 is 95319912.

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

It is not a de Polignac number, because 21991359 - 2⁷ = 21991231 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (39), and also a Moran number because the ratio is a prime number: 563881 = 21991359 / (2 + 1 + 9 + 9 + 1 + 3 + 5 + 9).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21991349) 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, 281902 + ... + 281979.

It is an arithmetic number, because the mean of its divisors is an integer number (3947174).

Almost surely, 2^21991359 is an apocalyptic number.

21991359 is a deficient number, since it is larger than the sum of its proper divisors (9586033).

21991359 is a wasteful number, since it uses less digits than its factorization.

21991359 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 563897.

The product of its digits is 21870, while the sum is 39.

The square root of 21991359 is about 4689.4945356616. The cubic root of 21991359 is about 280.1672427738.

The spelling of 21991359 in words is "twenty-one million, nine hundred ninety-one thousand, three hundred fifty-nine".