21450805 has 4 divisors (see below), whose sum is σ = 25740972. Its totient is φ = 17160640.

The previous prime is 21450799. The next prime is 21450809. The reversal of 21450805 is 50805412.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 14085009 + 7365796 = 3753^2 + 2714^2 .

It is not a de Polignac number, because 21450805 - 2³ = 21450797 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21450805.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21450809) 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 in 3 ways as a sum of consecutive naturals, for example, 2145076 + ... + 2145085.

It is an arithmetic number, because the mean of its divisors is an integer number (6435243).

Almost surely, 2^21450805 is an apocalyptic number.

It is an amenable number.

21450805 is a deficient number, since it is larger than the sum of its proper divisors (4290167).

21450805 is an equidigital number, since it uses as much as digits as its factorization.

21450805 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4290166.

The product of its (nonzero) digits is 1600, while the sum is 25.

The square root of 21450805 is about 4631.5013764437. The cubic root of 21450805 is about 277.8526426063.

The spelling of 21450805 in words is "twenty-one million, four hundred fifty thousand, eight hundred five".