21686945 has 16 divisors (see below), whose sum is σ = 29870208. Its totient is φ = 14807040.

The previous prime is 21686939. The next prime is 21686947. The reversal of 21686945 is 54968612.

It is a happy number.

It is not a de Polignac number, because 21686945 - 2¹² = 21682849 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21686947) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7790 + ... + 10200.

It is an arithmetic number, because the mean of its divisors is an integer number (1866888).

Almost surely, 2^21686945 is an apocalyptic number.

It is an amenable number.

21686945 is a deficient number, since it is larger than the sum of its proper divisors (8183263).

21686945 is a wasteful number, since it uses less digits than its factorization.

21686945 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2680.

The product of its digits is 103680, while the sum is 41.

The square root of 21686945 is about 4656.9244142460. The cubic root of 21686945 is about 278.8684991563.

The spelling of 21686945 in words is "twenty-one million, six hundred eighty-six thousand, nine hundred forty-five".