21805019 has 2 divisors, whose sum is σ = 21805020. Its totient is φ = 21805018.

The previous prime is 21805009. The next prime is 21805037. The reversal of 21805019 is 91050812.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21805019 is a prime.

It is a super-2 number, since 2×21805019² = 950917707180722, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21805009) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10902509 + 10902510.

It is an arithmetic number, because the mean of its divisors is an integer number (10902510).

Almost surely, 2^21805019 is an apocalyptic number.

21805019 is a deficient number, since it is larger than the sum of its proper divisors (1).

21805019 is an equidigital number, since it uses as much as digits as its factorization.

21805019 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 720, while the sum is 26.

The square root of 21805019 is about 4669.5844568869. The cubic root of 21805019 is about 279.3736808423.

The spelling of 21805019 in words is "twenty-one million, eight hundred five thousand, nineteen".