21391305 has 32 divisors (see below), whose sum is σ = 37140096. Its totient is φ = 10450944.

The previous prime is 21391303. The next prime is 21391309. The reversal of 21391305 is 50319312.

It is a happy number.

It is not a de Polignac number, because 21391305 - 2¹ = 21391303 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21391301) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 31449 + ... + 32121.

It is an arithmetic number, because the mean of its divisors is an integer number (1160628).

Almost surely, 2^21391305 is an apocalyptic number.

It is an amenable number.

21391305 is a deficient number, since it is larger than the sum of its proper divisors (15748791).

21391305 is a wasteful number, since it uses less digits than its factorization.

21391305 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 857.

The product of its (nonzero) digits is 810, while the sum is 24.

The square root of 21391305 is about 4625.0735129293. The cubic root of 21391305 is about 277.5955032049.

The spelling of 21391305 in words is "twenty-one million, three hundred ninety-one thousand, three hundred five".