20728705 has 8 divisors (see below), whose sum is σ = 24899112. Its totient is φ = 16566528.

The previous prime is 20728699. The next prime is 20728717. The reversal of 20728705 is 50782702.

It can be written as a sum of positive squares in 4 ways, for example, as 1218816 + 19509889 = 1104^2 + 4417^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 20728705 - 2⁷ = 20728577 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7719 + ... + 10051.

It is an arithmetic number, because the mean of its divisors is an integer number (3112389).

Almost surely, 2^20728705 is an apocalyptic number.

It is an amenable number.

20728705 is a deficient number, since it is larger than the sum of its proper divisors (4170407).

20728705 is a wasteful number, since it uses less digits than its factorization.

20728705 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4115.

The product of its (nonzero) digits is 7840, while the sum is 31.

The square root of 20728705 is about 4552.8787596421. The cubic root of 20728705 is about 274.6991972643.

The spelling of 20728705 in words is "twenty million, seven hundred twenty-eight thousand, seven hundred five".