21356423 has 16 divisors (see below), whose sum is σ = 24072576. Its totient is φ = 18779040.

The previous prime is 21356381. The next prime is 21356429. The reversal of 21356423 is 32465312.

It is a cyclic number.

It is not a de Polignac number, because 21356423 - 2¹⁸ = 21094279 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21356392 and 21356401.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21356429) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 76961 + ... + 77237.

It is an arithmetic number, because the mean of its divisors is an integer number (1504536).

Almost surely, 2^21356423 is an apocalyptic number.

21356423 is a deficient number, since it is larger than the sum of its proper divisors (2716153).

21356423 is a wasteful number, since it uses less digits than its factorization.

21356423 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 494.

The product of its digits is 4320, while the sum is 26.

The square root of 21356423 is about 4621.3010072922. The cubic root of 21356423 is about 277.4445329174. Note that the first 3 decimals are identical.

Subtracting 21356423 from its reverse (32465312), we obtain a square (11108889 = 3333²).

It can be divided in two parts, 2135 and 6423, that added together give a palindrome (8558).

The spelling of 21356423 in words is "twenty-one million, three hundred fifty-six thousand, four hundred twenty-three".