21530243221 has 2 divisors, whose sum is σ = 21530243222. Its totient is φ = 21530243220.

The previous prime is 21530243183. The next prime is 21530243239. The reversal of 21530243221 is 12234203512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19809155025 + 1721088196 = 140745^2 + 41486^2 .

It is a cyclic number.

It is not a de Polignac number, because 21530243221 - 2⁹ = 21530242709 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21530243321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10765121610 + 10765121611.

It is an arithmetic number, because the mean of its divisors is an integer number (10765121611).

Almost surely, 2^21530243221 is an apocalyptic number.

It is an amenable number.

21530243221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21530243221 is an equidigital number, since it uses as much as digits as its factorization.

21530243221 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2880, while the sum is 25.

Adding to 21530243221 its reverse (12234203512), we get a palindrome (33764446733).

The spelling of 21530243221 in words is "twenty-one billion, five hundred thirty million, two hundred forty-three thousand, two hundred twenty-one".