21630321 has 20 divisors (see below), whose sum is σ = 32656932. Its totient is φ = 14266368.

The previous prime is 21630289. The next prime is 21630337. The reversal of 21630321 is 12303612.

21630321 is a `hidden beast` number, since 2 + 1 + 630 + 32 + 1 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 15681600 + 5948721 = 3960^2 + 2439^2 .

It is not a de Polignac number, because 21630321 - 2⁵ = 21630289 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21630294 and 21630303.

It is not an unprimeable number, because it can be changed into a prime (21630391) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 6481 + ... + 9233.

Almost surely, 2^21630321 is an apocalyptic number.

It is an amenable number.

21630321 is a deficient number, since it is larger than the sum of its proper divisors (11026611).

21630321 is an equidigital number, since it uses as much as digits as its factorization.

21630321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2862 (or 2853 counting only the distinct ones).

The product of its (nonzero) digits is 216, while the sum is 18.

The square root of 21630321 is about 4650.8408917098. The cubic root of 21630321 is about 278.6255816953.

Adding to 21630321 its reverse (12303612), we get a palindrome (33933933).

The spelling of 21630321 in words is "twenty-one million, six hundred thirty thousand, three hundred twenty-one".