21420423 has 16 divisors (see below), whose sum is σ = 31810560. Its totient is φ = 14245848.

The previous prime is 21420403. The next prime is 21420433. The reversal of 21420423 is 32402412.

It is not a de Polignac number, because 21420423 - 2⁹ = 21419911 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21420396 and 21420405.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21420403) 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 15 ways as a sum of consecutive naturals, for example, 15736 + ... + 17042.

It is an arithmetic number, because the mean of its divisors is an integer number (1988160).

Almost surely, 2^21420423 is an apocalyptic number.

21420423 is a deficient number, since it is larger than the sum of its proper divisors (10390137).

21420423 is a wasteful number, since it uses less digits than its factorization.

21420423 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1923 (or 1917 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 18.

The square root of 21420423 is about 4628.2202842994. The cubic root of 21420423 is about 277.7214011040.

Adding to 21420423 its reverse (32402412), we get a palindrome (53822835).

The spelling of 21420423 in words is "twenty-one million, four hundred twenty thousand, four hundred twenty-three".