21641805 has 12 divisors (see below), whose sum is σ = 37512540. Its totient is φ = 11542272.

The previous prime is 21641797. The next prime is 21641831. The reversal of 21641805 is 50814612.

It can be written as a sum of positive squares in 2 ways, for example, as 4052169 + 17589636 = 2013^2 + 4194^2 .

It is not a de Polignac number, because 21641805 - 2³ = 21641797 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 240420 + ... + 240509.

It is an arithmetic number, because the mean of its divisors is an integer number (3126045).

Almost surely, 2^21641805 is an apocalyptic number.

It is an amenable number.

21641805 is a deficient number, since it is larger than the sum of its proper divisors (15870735).

21641805 is a wasteful number, since it uses less digits than its factorization.

21641805 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 480940 (or 480937 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 27.

The square root of 21641805 is about 4652.0753433280. The cubic root of 21641805 is about 278.6748823981.

It can be divided in two parts, 2164 and 1805, that added together give a square (3969 = 63²).

The spelling of 21641805 in words is "twenty-one million, six hundred forty-one thousand, eight hundred five".