21720619 has 4 divisors (see below), whose sum is σ = 22130496. Its totient is φ = 21310744.

The previous prime is 21720617. The next prime is 21720631. The reversal of 21720619 is 91602712.

It is a happy number.

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 21720619 - 2¹ = 21720617 is a prime.

It is a super-2 number, since 2×21720619² = 943570579486322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21720613) 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, 204859 + ... + 204964.

It is an arithmetic number, because the mean of its divisors is an integer number (5532624).

Almost surely, 2^21720619 is an apocalyptic number.

21720619 is a deficient number, since it is larger than the sum of its proper divisors (409877).

21720619 is an equidigital number, since it uses as much as digits as its factorization.

21720619 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 409876.

The product of its (nonzero) digits is 1512, while the sum is 28.

The square root of 21720619 is about 4660.5384882007. The cubic root of 21720619 is about 279.0127604720.

The spelling of 21720619 in words is "twenty-one million, seven hundred twenty thousand, six hundred nineteen".