21987019 has 2 divisors, whose sum is σ = 21987020. Its totient is φ = 21987018.

The previous prime is 21986989. The next prime is 21987041. The reversal of 21987019 is 91078912.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21987019 - 2⁹ = 21986507 is a prime.

It is a super-2 number, since 2×21987019² = 966858009012722, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21987059) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10993509 + 10993510.

It is an arithmetic number, because the mean of its divisors is an integer number (10993510).

Almost surely, 2^21987019 is an apocalyptic number.

21987019 is a deficient number, since it is larger than the sum of its proper divisors (1).

21987019 is an equidigital number, since it uses as much as digits as its factorization.

21987019 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 9072, while the sum is 37.

The square root of 21987019 is about 4689.0317763905. The cubic root of 21987019 is about 280.1488112036.

It can be divided in two parts, 2 and 1987019, that added together give a triangular number (1987021 = T₁₉₉₃).

The spelling of 21987019 in words is "twenty-one million, nine hundred eighty-seven thousand, nineteen".