21407891 has 2 divisors, whose sum is σ = 21407892. Its totient is φ = 21407890.

The previous prime is 21407821. The next prime is 21407899. The reversal of 21407891 is 19870412.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21407891 is a prime.

It is not a weakly prime, because it can be changed into another prime (21407899) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10703945 + 10703946.

It is an arithmetic number, because the mean of its divisors is an integer number (10703946).

Almost surely, 2^21407891 is an apocalyptic number.

21407891 is a deficient number, since it is larger than the sum of its proper divisors (1).

21407891 is an equidigital number, since it uses as much as digits as its factorization.

21407891 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4032, while the sum is 32.

The square root of 21407891 is about 4626.8662180789. The cubic root of 21407891 is about 277.6672303164.

The spelling of 21407891 in words is "twenty-one million, four hundred seven thousand, eight hundred ninety-one".