21247 has 2 divisors, whose sum is σ = 21248. Its totient is φ = 21246.

The previous prime is 21227. The next prime is 21269. The reversal of 21247 is 74212.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21247 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21247.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21227) 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, 10623 + 10624.

It is an arithmetic number, because the mean of its divisors is an integer number (10624).

2²¹²⁴⁷ is an apocalyptic number.

21247 is a deficient number, since it is larger than the sum of its proper divisors (1).

21247 is an equidigital number, since it uses as much as digits as its factorization.

21247 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 112, while the sum is 16.

The square root of 21247 is about 145.7635070928. The cubic root of 21247 is about 27.6969877734.

Adding to 21247 its reverse (74212), we get a palindrome (95459).

The spelling of 21247 in words is "twenty-one thousand, two hundred forty-seven", and thus it is an iban number.