21720019 has 4 divisors (see below), whose sum is σ = 21736440. Its totient is φ = 21703600.

The previous prime is 21720007. The next prime is 21720047. The reversal of 21720019 is 91002712.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21720019 - 2¹³ = 21711827 is a prime.

It is a super-2 number, since 2×21720019² = 943518450720722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21723019) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6034 + ... + 8935.

It is an arithmetic number, because the mean of its divisors is an integer number (5434110).

Almost surely, 2^21720019 is an apocalyptic number.

21720019 is a deficient number, since it is larger than the sum of its proper divisors (16421).

21720019 is a wasteful number, since it uses less digits than its factorization.

21720019 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16420.

The product of its (nonzero) digits is 252, while the sum is 22.

The square root of 21720019 is about 4660.4741175121. The cubic root of 21720019 is about 279.0101913433.

The spelling of 21720019 in words is "twenty-one million, seven hundred twenty thousand, nineteen".