21621023 has 4 divisors (see below), whose sum is σ = 21975528. Its totient is φ = 21266520.

The previous prime is 21621013. The next prime is 21621029. The reversal of 21621023 is 32012612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21621023 - 2⁴ = 21621007 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21620992 and 21621010.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21621029) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 177161 + ... + 177282.

It is an arithmetic number, because the mean of its divisors is an integer number (5493882).

Almost surely, 2^21621023 is an apocalyptic number.

21621023 is a deficient number, since it is larger than the sum of its proper divisors (354505).

21621023 is an equidigital number, since it uses as much as digits as its factorization.

21621023 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 354504.

The product of its (nonzero) digits is 144, while the sum is 17.

The square root of 21621023 is about 4649.8411800835. The cubic root of 21621023 is about 278.5856526847.

Adding to 21621023 its reverse (32012612), we get a palindrome (53633635).

The spelling of 21621023 in words is "twenty-one million, six hundred twenty-one thousand, twenty-three".