21478805 has 4 divisors (see below), whose sum is σ = 25774572. Its totient is φ = 17183040.

The previous prime is 21478799. The next prime is 21478817. The reversal of 21478805 is 50887412.

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 6041764 + 15437041 = 2458^2 + 3929^2 .

It is not a de Polignac number, because 21478805 - 2⁴ = 21478789 is a prime.

It is a super-2 number, since 2×21478805² = 922678128456050, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2147876 + ... + 2147885.

It is an arithmetic number, because the mean of its divisors is an integer number (6443643).

Almost surely, 2^21478805 is an apocalyptic number.

It is an amenable number.

21478805 is a deficient number, since it is larger than the sum of its proper divisors (4295767).

21478805 is an equidigital number, since it uses as much as digits as its factorization.

21478805 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4295766.

The product of its (nonzero) digits is 17920, while the sum is 35.

The square root of 21478805 is about 4634.5231685687. The cubic root of 21478805 is about 277.9734848682.

The spelling of 21478805 in words is "twenty-one million, four hundred seventy-eight thousand, eight hundred five".