21530387 has 2 divisors, whose sum is σ = 21530388. Its totient is φ = 21530386.

The previous prime is 21530329. The next prime is 21530389. The reversal of 21530387 is 78303512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21530387 - 2¹² = 21526291 is a prime.

Together with 21530389, it forms a pair of twin primes.

It is a Chen prime.

It is equal to p_1361369 and since 21530387 and 1361369 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 (21530389) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10765193 + 10765194.

It is an arithmetic number, because the mean of its divisors is an integer number (10765194).

Almost surely, 2^21530387 is an apocalyptic number.

21530387 is a deficient number, since it is larger than the sum of its proper divisors (1).

21530387 is an equidigital number, since it uses as much as digits as its factorization.

21530387 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 5040, while the sum is 29.

The square root of 21530387 is about 4640.0848052595. The cubic root of 21530387 is about 278.1958275533.

Adding to 21530387 its reverse (78303512), we get a palindrome (99833899).

The spelling of 21530387 in words is "twenty-one million, five hundred thirty thousand, three hundred eighty-seven".