21686123 has 2 divisors, whose sum is σ = 21686124. Its totient is φ = 21686122.

The previous prime is 21686111. The next prime is 21686177. The reversal of 21686123 is 32168612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21686123 - 2¹² = 21682027 is a prime.

It is a super-2 number, since 2×21686123² = 940575861542258, which contains 22 as substring.

It is a Sophie Germain prime.

It is not a weakly prime, because it can be changed into another prime (21686023) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10843061 + 10843062.

It is an arithmetic number, because the mean of its divisors is an integer number (10843062).

Almost surely, 2^21686123 is an apocalyptic number.

21686123 is a deficient number, since it is larger than the sum of its proper divisors (1).

21686123 is an equidigital number, since it uses as much as digits as its factorization.

21686123 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3456, while the sum is 29.

The square root of 21686123 is about 4656.8361577363. The cubic root of 21686123 is about 278.8649757954.

The spelling of 21686123 in words is "twenty-one million, six hundred eighty-six thousand, one hundred twenty-three".