20687205557 has 4 divisors (see below), whose sum is σ = 20705148780. Its totient is φ = 20669262336.

The previous prime is 20687205509. The next prime is 20687205569. The reversal of 20687205557 is 75550278602.

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 16722110596 + 3965094961 = 129314^2 + 62969^2 .

It is a cyclic number.

It is not a de Polignac number, because 20687205557 - 2¹⁰ = 20687204533 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20687205587) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8969882 + ... + 8972187.

It is an arithmetic number, because the mean of its divisors is an integer number (5176287195).

Almost surely, 2^20687205557 is an apocalyptic number.

It is an amenable number.

20687205557 is a deficient number, since it is larger than the sum of its proper divisors (17943223).

20687205557 is a wasteful number, since it uses less digits than its factorization.

20687205557 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17943222.

The product of its (nonzero) digits is 1176000, while the sum is 47.

The spelling of 20687205557 in words is "twenty billion, six hundred eighty-seven million, two hundred five thousand, five hundred fifty-seven".