21686719 has 4 divisors (see below), whose sum is σ = 21930480. Its totient is φ = 21442960.

The previous prime is 21686671. The next prime is 21686741. The reversal of 21686719 is 91768612.

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

It is a cyclic number.

It is not a de Polignac number, because 21686719 - 2⁷ = 21686591 is a prime.

It is a super-2 number, since 2×21686719² = 940627561969922, which contains 22 as substring.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21686219) 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, 121747 + ... + 121924.

It is an arithmetic number, because the mean of its divisors is an integer number (5482620).

Almost surely, 2^21686719 is an apocalyptic number.

21686719 is a deficient number, since it is larger than the sum of its proper divisors (243761).

21686719 is an equidigital number, since it uses as much as digits as its factorization.

21686719 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 243760.

The product of its digits is 36288, while the sum is 40.

The square root of 21686719 is about 4656.9001492409. The cubic root of 21686719 is about 278.8675304552.

The spelling of 21686719 in words is "twenty-one million, six hundred eighty-six thousand, seven hundred nineteen".