21587 has 2 divisors, whose sum is σ = 21588. Its totient is φ = 21586.

The previous prime is 21577. The next prime is 21589. The reversal of 21587 is 78512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21587 - 2⁶ = 21523 is a prime.

It is a super-3 number, since 3×21587³ = 30178533327009, which contains 333 as substring.

Together with 21589, it forms a pair of twin primes.

It is a Chen prime.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 21587.

It is not a weakly prime, because it can be changed into another prime (21589) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10793 + 10794.

It is an arithmetic number, because the mean of its divisors is an integer number (10794).

2²¹⁵⁸⁷ is an apocalyptic number.

21587 is a deficient number, since it is larger than the sum of its proper divisors (1).

21587 is an equidigital number, since it uses as much as digits as its factorization.

21587 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 560, while the sum is 23.

The square root of 21587 is about 146.9251510123. The cubic root of 21587 is about 27.8439447828.

The spelling of 21587 in words is "twenty-one thousand, five hundred eighty-seven".