21686671 has 2 divisors, whose sum is σ = 21686672. Its totient is φ = 21686670.

The previous prime is 21686669. The next prime is 21686741. The reversal of 21686671 is 17668612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21686671 - 2¹ = 21686669 is a prime.

Together with 21686669, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21686671.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21686471) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10843335 + 10843336.

It is an arithmetic number, because the mean of its divisors is an integer number (10843336).

Almost surely, 2^21686671 is an apocalyptic number.

21686671 is a deficient number, since it is larger than the sum of its proper divisors (1).

21686671 is an equidigital number, since it uses as much as digits as its factorization.

21686671 is an evil number, because the sum of its binary digits is even.

The product of its digits is 24192, while the sum is 37.

The square root of 21686671 is about 4656.8949955952. The cubic root of 21686671 is about 278.8673247126.

The spelling of 21686671 in words is "twenty-one million, six hundred eighty-six thousand, six hundred seventy-one".