21305223 has 12 divisors (see below), whose sum is σ = 30820608. Its totient is φ = 14182080.

The previous prime is 21305209. The next prime is 21305231. The reversal of 21305223 is 32250312.

It is not a de Polignac number, because 21305223 - 2⁵ = 21305191 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21305196 and 21305205.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21305203) 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, 6586 + ... + 9272.

It is an arithmetic number, because the mean of its divisors is an integer number (2568384).

Almost surely, 2^21305223 is an apocalyptic number.

21305223 is a deficient number, since it is larger than the sum of its proper divisors (9515385).

21305223 is a wasteful number, since it uses less digits than its factorization.

21305223 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3574 (or 3571 counting only the distinct ones).

The product of its (nonzero) digits is 360, while the sum is 18.

The square root of 21305223 is about 4615.7581175794. The cubic root of 21305223 is about 277.2226398430. Note that the first 3 decimals are identical.

Adding to 21305223 its reverse (32250312), we get a palindrome (53555535).

It can be divided in two parts, 21305 and 223, that added together give a triangular number (21528 = T₂₀₇).

The spelling of 21305223 in words is "twenty-one million, three hundred five thousand, two hundred twenty-three".