21187 has 2 divisors, whose sum is σ = 21188. Its totient is φ = 21186.

The previous prime is 21179. The next prime is 21191. The reversal of 21187 is 78112.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21187 - 2³ = 21179 is a prime.

It is not a weakly prime, because it can be changed into another prime (21107) 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, 10593 + 10594.

It is an arithmetic number, because the mean of its divisors is an integer number (10594).

2²¹¹⁸⁷ is an apocalyptic number.

21187 is a deficient number, since it is larger than the sum of its proper divisors (1).

21187 is an equidigital number, since it uses as much as digits as its factorization.

21187 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 112, while the sum is 19.

The square root of 21187 is about 145.5575487565. The cubic root of 21187 is about 27.6708917597.

Adding to 21187 its reverse (78112), we get a palindrome (99299).

The spelling of 21187 in words is "twenty-one thousand, one hundred eighty-seven".