21505019 has 2 divisors, whose sum is σ = 21505020. Its totient is φ = 21505018.

The previous prime is 21505013. The next prime is 21505039. The reversal of 21505019 is 91050512.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21505019 is a prime.

It is a super-2 number, since 2×21505019² = 924931684380722, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21504985 and 21505003.

It is not a weakly prime, because it can be changed into another prime (21505013) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10752509 + 10752510.

It is an arithmetic number, because the mean of its divisors is an integer number (10752510).

Almost surely, 2^21505019 is an apocalyptic number.

21505019 is a deficient number, since it is larger than the sum of its proper divisors (1).

21505019 is an equidigital number, since it uses as much as digits as its factorization.

21505019 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 450, while the sum is 23.

The square root of 21505019 is about 4637.3504288548. The cubic root of 21505019 is about 278.0865239709.

The spelling of 21505019 in words is "twenty-one million, five hundred five thousand, nineteen".