21530233 has 2 divisors, whose sum is σ = 21530234. Its totient is φ = 21530232.

The previous prime is 21530227. The next prime is 21530237. The reversal of 21530233 is 33203512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21409129 + 121104 = 4627^2 + 348^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21530233 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21530233.

It is not a weakly prime, because it can be changed into another prime (21530237) 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 as a sum of consecutive naturals, namely, 10765116 + 10765117.

It is an arithmetic number, because the mean of its divisors is an integer number (10765117).

Almost surely, 2^21530233 is an apocalyptic number.

It is an amenable number.

21530233 is a deficient number, since it is larger than the sum of its proper divisors (1).

21530233 is an equidigital number, since it uses as much as digits as its factorization.

21530233 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 540, while the sum is 19.

The square root of 21530233 is about 4640.0682107055. The cubic root of 21530233 is about 278.1951642697.

Adding to 21530233 its reverse (33203512), we get a palindrome (54733745).

The spelling of 21530233 in words is "twenty-one million, five hundred thirty thousand, two hundred thirty-three".