21686237 has 4 divisors (see below), whose sum is σ = 22961916. Its totient is φ = 20410560.

The previous prime is 21686227. The next prime is 21686243. The reversal of 21686237 is 73268612.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 8826841 + 12859396 = 2971^2 + 3586^2 .

It is a cyclic number.

It is not a de Polignac number, because 21686237 - 2⁴ = 21686221 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21686197 and 21686206.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21686207) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 637814 + ... + 637847.

It is an arithmetic number, because the mean of its divisors is an integer number (5740479).

Almost surely, 2^21686237 is an apocalyptic number.

It is an amenable number.

21686237 is a deficient number, since it is larger than the sum of its proper divisors (1275679).

21686237 is a wasteful number, since it uses less digits than its factorization.

21686237 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1275678.

The product of its digits is 24192, while the sum is 35.

The square root of 21686237 is about 4656.8483977901. The cubic root of 21686237 is about 278.8654644420.

The spelling of 21686237 in words is "twenty-one million, six hundred eighty-six thousand, two hundred thirty-seven".