21729619 has 4 divisors (see below), whose sum is σ = 22316944. Its totient is φ = 21142296.

The previous prime is 21729611. The next prime is 21729637. The reversal of 21729619 is 91692712.

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 21729619 - 2³ = 21729611 is a prime.

It is a super-2 number, since 2×21729619² = 944352683770322, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (37), and also a Moran number because the ratio is a prime number: 587287 = 21729619 / (2 + 1 + 7 + 2 + 9 + 6 + 1 + 9).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21729611) 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, 293607 + ... + 293680.

It is an arithmetic number, because the mean of its divisors is an integer number (5579236).

Almost surely, 2^21729619 is an apocalyptic number.

21729619 is a deficient number, since it is larger than the sum of its proper divisors (587325).

21729619 is an equidigital number, since it uses as much as digits as its factorization.

21729619 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 587324.

The product of its digits is 13608, while the sum is 37.

The square root of 21729619 is about 4661.5039418625. The cubic root of 21729619 is about 279.0512917265.

The spelling of 21729619 in words is "twenty-one million, seven hundred twenty-nine thousand, six hundred nineteen".