21688523 has 2 divisors, whose sum is σ = 21688524. Its totient is φ = 21688522.

The previous prime is 21688483. The next prime is 21688531. The reversal of 21688523 is 32588612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21688523 - 2¹⁰ = 21687499 is a prime.

It is not a weakly prime, because it can be changed into another prime (21688543) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10844261 + 10844262.

It is an arithmetic number, because the mean of its divisors is an integer number (10844262).

Almost surely, 2^21688523 is an apocalyptic number.

21688523 is a deficient number, since it is larger than the sum of its proper divisors (1).

21688523 is an equidigital number, since it uses as much as digits as its factorization.

21688523 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 23040, while the sum is 35.

The square root of 21688523 is about 4657.0938362889. The cubic root of 21688523 is about 278.8752627310.

The spelling of 21688523 in words is "twenty-one million, six hundred eighty-eight thousand, five hundred twenty-three".