21330891 has 8 divisors (see below), whose sum is σ = 31601360. Its totient is φ = 14220576.

The previous prime is 21330889. The next prime is 21330899. The reversal of 21330891 is 19803312.

It is not a de Polignac number, because 21330891 - 2¹ = 21330889 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 790033 = 21330891 / (2 + 1 + 3 + 3 + 0 + 8 + 9 + 1).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21330899) 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, 394990 + ... + 395043.

It is an arithmetic number, because the mean of its divisors is an integer number (3950170).

Almost surely, 2^21330891 is an apocalyptic number.

21330891 is a deficient number, since it is larger than the sum of its proper divisors (10270469).

21330891 is an equidigital number, since it uses as much as digits as its factorization.

21330891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 790042 (or 790036 counting only the distinct ones).

The product of its (nonzero) digits is 1296, while the sum is 27.

The square root of 21330891 is about 4618.5377556105. The cubic root of 21330891 is about 277.3339254654. Note that the first 3 decimals are identical.

The spelling of 21330891 in words is "twenty-one million, three hundred thirty thousand, eight hundred ninety-one".