21530291 has 2 divisors, whose sum is σ = 21530292. Its totient is φ = 21530290.

The previous prime is 21530281. The next prime is 21530293. The reversal of 21530291 is 19203512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21530291 - 2⁶ = 21530227 is a prime.

Together with 21530293, it forms a pair of twin primes.

It is a Chen prime.

It is equal to p_1361363 and since 21530291 and 1361363 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 (21530293) 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, 10765145 + 10765146.

It is an arithmetic number, because the mean of its divisors is an integer number (10765146).

Almost surely, 2^21530291 is an apocalyptic number.

21530291 is a deficient number, since it is larger than the sum of its proper divisors (1).

21530291 is an equidigital number, since it uses as much as digits as its factorization.

21530291 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 23.

The square root of 21530291 is about 4640.0744606094. The cubic root of 21530291 is about 278.1954140782.

The spelling of 21530291 in words is "twenty-one million, five hundred thirty thousand, two hundred ninety-one".