21687205 has 8 divisors (see below), whose sum is σ = 26381592. Its totient is φ = 17111808.

The previous prime is 21687203. The next prime is 21687221. The reversal of 21687205 is 50278612.

It can be written as a sum of positive squares in 4 ways, for example, as 4901796 + 16785409 = 2214^2 + 4097^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21687205 - 2¹ = 21687203 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21687203) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 29344 + ... + 30073.

It is an arithmetic number, because the mean of its divisors is an integer number (3297699).

Almost surely, 2^21687205 is an apocalyptic number.

It is an amenable number.

21687205 is a deficient number, since it is larger than the sum of its proper divisors (4694387).

21687205 is an equidigital number, since it uses as much as digits as its factorization.

21687205 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 59495.

The product of its (nonzero) digits is 6720, while the sum is 31.

The square root of 21687205 is about 4656.9523295821. The cubic root of 21687205 is about 278.8696135828.

The spelling of 21687205 in words is "twenty-one million, six hundred eighty-seven thousand, two hundred five".