20729809 has 9 divisors (see below), whose sum is σ = 21606897. Its totient is φ = 19887504.

The previous prime is 20729789. The next prime is 20729861. The reversal of 20729809 is 90892702.

The square root of 20729809 is 4553.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in 4 ways, for example, as 731025 + 19998784 = 855^2 + 4472^2 .

It is a de Polignac number, because none of the positive numbers 2^k-20729809 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20729909) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 131959 + ... + 132115.

Almost surely, 2^20729809 is an apocalyptic number.

20729809 is a gapful number since it is divisible by the number (29) formed by its first and last digit.

20729809 is the 4553-rd square number.

20729809 is the 2277-th centered octagonal number.

It is an amenable number.

20729809 is a deficient number, since it is larger than the sum of its proper divisors (877088).

20729809 is an frugal number, since it uses more digits than its factorization.

20729809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 372 (or 186 counting only the distinct ones).

The product of its (nonzero) digits is 18144, while the sum is 37.

The cubic root of 20729809 is about 274.7040739563.

It can be divided in two parts, 2072 and 9809, that added together give a square (11881 = 109²).

The spelling of 20729809 in words is "twenty million, seven hundred twenty-nine thousand, eight hundred nine".