21681423 has 12 divisors (see below), whose sum is σ = 31596240. Its totient is φ = 14325696.

The previous prime is 21681421. The next prime is 21681449. The reversal of 21681423 is 32418612.

It is not a de Polignac number, because 21681423 - 2¹ = 21681421 is a prime.

It is a Smith number, since the sum of its digits (27) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21681421) 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 11 ways as a sum of consecutive naturals, for example, 9643 + ... + 11676.

It is an arithmetic number, because the mean of its divisors is an integer number (2633020).

Almost surely, 2^21681423 is an apocalyptic number.

21681423 is a deficient number, since it is larger than the sum of its proper divisors (9914817).

21681423 is a wasteful number, since it uses less digits than its factorization.

21681423 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21438 (or 21435 counting only the distinct ones).

The product of its digits is 2304, while the sum is 27.

The square root of 21681423 is about 4656.3314959311. The cubic root of 21681423 is about 278.8448283477.

The spelling of 21681423 in words is "twenty-one million, six hundred eighty-one thousand, four hundred twenty-three".