21123621 has 12 divisors (see below), whose sum is σ = 31222048. Its totient is φ = 13754664.

The previous prime is 21123607. The next prime is 21123631. The reversal of 21123621 is 12632112.

21123621 is a `hidden beast` number, since 21 + 1 + 23 + 621 = 666.

It is not a de Polignac number, because 21123621 - 2⁵ = 21123589 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21123594 and 21123603.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21123631) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 26905 + ... + 27678.

Almost surely, 2^21123621 is an apocalyptic number.

It is an amenable number.

21123621 is a deficient number, since it is larger than the sum of its proper divisors (10098427).

21123621 is a wasteful number, since it uses less digits than its factorization.

21123621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 54632 (or 54629 counting only the distinct ones).

The product of its digits is 144, while the sum is 18.

The square root of 21123621 is about 4596.0440598410. The cubic root of 21123621 is about 276.4327254205.

Adding to 21123621 its reverse (12632112), we get a palindrome (33755733).

It can be divided in two parts, 211 and 23621, that added together give a palindrome (23832).

The spelling of 21123621 in words is "twenty-one million, one hundred twenty-three thousand, six hundred twenty-one".