21645687 has 16 divisors (see below), whose sum is σ = 34122240. Its totient is φ = 11942112.

The previous prime is 21645683. The next prime is 21645697. The reversal of 21645687 is 78654612.

It is not a de Polignac number, because 21645687 - 2² = 21645683 is a prime.

It is a plaindrome in base 8.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21645683) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 17163 + ... + 18380.

It is an arithmetic number, because the mean of its divisors is an integer number (2132640).

Almost surely, 2^21645687 is an apocalyptic number.

21645687 is a deficient number, since it is larger than the sum of its proper divisors (12476553).

21645687 is a wasteful number, since it uses less digits than its factorization.

21645687 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 35582.

The product of its digits is 80640, while the sum is 39.

The square root of 21645687 is about 4652.4925577587. The cubic root of 21645687 is about 278.6915438429.

The spelling of 21645687 in words is "twenty-one million, six hundred forty-five thousand, six hundred eighty-seven".