21720569 has 4 divisors (see below), whose sum is σ = 23391396. Its totient is φ = 20049744.

The previous prime is 21720563. The next prime is 21720571. The reversal of 21720569 is 96502712.

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

It can be written as a sum of positive squares in 2 ways, for example, as 4787344 + 16933225 = 2188^2 + 4115^2 .

It is not a de Polignac number, because 21720569 - 2¹⁶ = 21655033 is a prime.

It is a super-2 number, since 2×21720569² = 943566235367522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21720563) 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, 835394 + ... + 835419.

It is an arithmetic number, because the mean of its divisors is an integer number (5847849).

Almost surely, 2^21720569 is an apocalyptic number.

It is an amenable number.

21720569 is a deficient number, since it is larger than the sum of its proper divisors (1670827).

21720569 is a wasteful number, since it uses less digits than its factorization.

21720569 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1670826.

The product of its (nonzero) digits is 7560, while the sum is 32.

The square root of 21720569 is about 4660.5331240106. The cubic root of 21720569 is about 279.0125463798.

The spelling of 21720569 in words is "twenty-one million, seven hundred twenty thousand, five hundred sixty-nine".