21351623 has 4 divisors (see below), whose sum is σ = 21361128. Its totient is φ = 21342120.

The previous prime is 21351619. The next prime is 21351637. The reversal of 21351623 is 32615312.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21351623 - 2² = 21351619 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21311623) 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 3 ways as a sum of consecutive naturals, for example, 713 + ... + 6573.

It is an arithmetic number, because the mean of its divisors is an integer number (5340282).

Almost surely, 2^21351623 is an apocalyptic number.

21351623 is a deficient number, since it is larger than the sum of its proper divisors (9505).

21351623 is an equidigital number, since it uses as much as digits as its factorization.

21351623 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9504.

The product of its digits is 1080, while the sum is 23.

The square root of 21351623 is about 4620.7816438347. The cubic root of 21351623 is about 277.4237455171.

Adding to 21351623 its reverse (32615312), we get a palindrome (53966935).

The spelling of 21351623 in words is "twenty-one million, three hundred fifty-one thousand, six hundred twenty-three".