21019 has 2 divisors, whose sum is σ = 21020. Its totient is φ = 21018.

The previous prime is 21017. The next prime is 21023. The reversal of 21019 is 91012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21019 - 2¹ = 21017 is a prime.

It is a super-2 number, since 2×21019² = 883596722, which contains 22 as substring.

Together with 21017, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21011) 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, 10509 + 10510.

It is an arithmetic number, because the mean of its divisors is an integer number (10510).

2²¹⁰¹⁹ is an apocalyptic number.

21019 is a deficient number, since it is larger than the sum of its proper divisors (1).

21019 is an equidigital number, since it uses as much as digits as its factorization.

21019 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 18, while the sum is 13.

The square root of 21019 is about 144.9793088685. The cubic root of 21019 is about 27.5975598207.

The spelling of 21019 in words is "twenty-one thousand, nineteen".