21686825 has 12 divisors (see below), whose sum is σ = 27760128. Its totient is φ = 16789200.

The previous prime is 21686813. The next prime is 21686851. The reversal of 21686825 is 52868612.

It is not a de Polignac number, because 21686825 - 2¹⁰ = 21685801 is a prime.

It is a hoax number, since the sum of its digits (38) coincides with the sum of the digits of its distinct prime factors.

It is a Curzon 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, 13217 + ... + 14766.

It is an arithmetic number, because the mean of its divisors is an integer number (2313344).

Almost surely, 2^21686825 is an apocalyptic number.

21686825 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21686825 is a deficient number, since it is larger than the sum of its proper divisors (6073303).

21686825 is a wasteful number, since it uses less digits than its factorization.

21686825 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 28024 (or 28019 counting only the distinct ones).

The product of its digits is 46080, while the sum is 38.

The square root of 21686825 is about 4656.9115301882. The cubic root of 21686825 is about 278.8679848026.

The spelling of 21686825 in words is "twenty-one million, six hundred eighty-six thousand, eight hundred twenty-five".