21686691 has 8 divisors (see below), whose sum is σ = 31139920. Its totient is φ = 13345632.

The previous prime is 21686671. The next prime is 21686741. The reversal of 21686691 is 19668612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21686691 - 2⁷ = 21686563 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (39), and also a Moran number because the ratio is a prime number: 556069 = 21686691 / (2 + 1 + 6 + 8 + 6 + 6 + 9 + 1).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21686671) 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 7 ways as a sum of consecutive naturals, for example, 277996 + ... + 278073.

It is an arithmetic number, because the mean of its divisors is an integer number (3892490).

Almost surely, 2^21686691 is an apocalyptic number.

21686691 is a deficient number, since it is larger than the sum of its proper divisors (9453229).

21686691 is a wasteful number, since it uses less digits than its factorization.

21686691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 556085.

The product of its digits is 31104, while the sum is 39.

The square root of 21686691 is about 4656.8971429483. The cubic root of 21686691 is about 278.8674104387.

The spelling of 21686691 in words is "twenty-one million, six hundred eighty-six thousand, six hundred ninety-one".