21530281 has 2 divisors, whose sum is σ = 21530282. Its totient is φ = 21530280.

The previous prime is 21530261. The next prime is 21530291. The reversal of 21530281 is 18203512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15280281 + 6250000 = 3909^2 + 2500^2 .

It is a cyclic number.

It is not a de Polignac number, because 21530281 - 2⁷ = 21530153 is a prime.

It is a super-2 number, since 2×21530281² = 927105999877922, which contains 22 as substring.

It is equal to p_1361362 and since 21530281 and 1361362 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (21530251) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10765140 + 10765141.

It is an arithmetic number, because the mean of its divisors is an integer number (10765141).

Almost surely, 2^21530281 is an apocalyptic number.

It is an amenable number.

21530281 is a deficient number, since it is larger than the sum of its proper divisors (1).

21530281 is an equidigital number, since it uses as much as digits as its factorization.

21530281 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 480, while the sum is 22.

The square root of 21530281 is about 4640.0733830404. The cubic root of 21530281 is about 278.1953710078.

Adding to 21530281 its reverse (18203512), we get a palindrome (39733793).

The spelling of 21530281 in words is "twenty-one million, five hundred thirty thousand, two hundred eighty-one".