21678823 has 2 divisors, whose sum is σ = 21678824. Its totient is φ = 21678822.

The previous prime is 21678809. The next prime is 21678907. The reversal of 21678823 is 32887612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21678823 - 2¹⁷ = 21547751 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21678623) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10839411 + 10839412.

It is an arithmetic number, because the mean of its divisors is an integer number (10839412).

Almost surely, 2^21678823 is an apocalyptic number.

21678823 is a deficient number, since it is larger than the sum of its proper divisors (1).

21678823 is an equidigital number, since it uses as much as digits as its factorization.

21678823 is an evil number, because the sum of its binary digits is even.

The product of its digits is 32256, while the sum is 37.

The square root of 21678823 is about 4656.0522978163. The cubic root of 21678823 is about 278.8336817003.

It can be divided in two parts, 216788 and 23, that added together give a triangular number (216811 = T₆₅₈).

The spelling of 21678823 in words is "twenty-one million, six hundred seventy-eight thousand, eight hundred twenty-three".