21721579 has 16 divisors (see below), whose sum is σ = 25534080. Its totient is φ = 18264960.

The previous prime is 21721577. The next prime is 21721621. The reversal of 21721579 is 97512712.

It is a cyclic number.

It is not a de Polignac number, because 21721579 - 2¹ = 21721577 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21721577) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7779 + ... + 10195.

It is an arithmetic number, because the mean of its divisors is an integer number (1595880).

Almost surely, 2^21721579 is an apocalyptic number.

21721579 is a deficient number, since it is larger than the sum of its proper divisors (3812501).

21721579 is a wasteful number, since it uses less digits than its factorization.

21721579 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2490.

The product of its digits is 8820, while the sum is 34.

The square root of 21721579 is about 4660.6414794532. The cubic root of 21721579 is about 279.0168709796.

The spelling of 21721579 in words is "twenty-one million, seven hundred twenty-one thousand, five hundred seventy-nine".