20851123087809 has 45 divisors (see below), whose sum is σ = 36233857413171. Its totient is φ = 11914763091840.

The previous prime is 20851123087789. The next prime is 20851123087813. The reversal of 20851123087809 is 90878032115802.

The square root of 20851123087809 is 4566303.

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

20851123087809 is a `hidden beast` number, since 20 + 8 + 511 + 2 + 30 + 8 + 78 + 0 + 9 = 666.

It can be written as a sum of positive squares in only one way, i.e., 7572970121409 + 13278152966400 = 2751903^2 + 3643920^2 .

It is not a de Polignac number, because 20851123087809 - 2¹¹ = 20851123085761 is a prime.

It is not an unprimeable number, because it can be changed into a prime (20851123087829) by changing a digit.

It is a polite number, since it can be written in 44 ways as a sum of consecutive naturals, for example, 287640849 + ... + 287713329.

Almost surely, 2^{20851123087809} is an apocalyptic number.

20851123087809 is the 4566303-rd square number.

20851123087809 is the 2283152-nd centered octagonal number.

It is an amenable number.

20851123087809 is a deficient number, since it is larger than the sum of its proper divisors (15382734325362).

20851123087809 is an frugal number, since it uses more digits than its factorization.

20851123087809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 144988 (or 72491 counting only the distinct ones).

The product of its (nonzero) digits is 1935360, while the sum is 54.

The spelling of 20851123087809 in words is "twenty trillion, eight hundred fifty-one billion, one hundred twenty-three million, eighty-seven thousand, eight hundred nine".