21505404 has 12 divisors (see below), whose sum is σ = 50179304. Its totient is φ = 7168464.

The previous prime is 21505381. The next prime is 21505417. The reversal of 21505404 is 40450512.

It is a tau number, because it is divible by the number of its divisors (12).

It is a congruent number.

It is an unprimeable number.

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, 896047 + ... + 896070.

Almost surely, 2^21505404 is an apocalyptic number.

It is an amenable number.

21505404 is an abundant number, since it is smaller than the sum of its proper divisors (28673900).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21505404 is a wasteful number, since it uses less digits than its factorization.

21505404 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1792124 (or 1792122 counting only the distinct ones).

The product of its (nonzero) digits is 800, while the sum is 21.

The square root of 21505404 is about 4637.3919394418. The cubic root of 21505404 is about 278.0881834699.

Adding to 21505404 its reverse (40450512), we get a palindrome (61955916).

The spelling of 21505404 in words is "twenty-one million, five hundred five thousand, four hundred four".