206778787821 has 20 divisors (see below), whose sum is σ = 309131562300. Its totient is φ = 137745510336.

The previous prime is 206778787781. The next prime is 206778787879. The reversal of 206778787821 is 128787877602.

It can be written as a sum of positive squares in 2 ways, for example, as 69319517796 + 137459270025 = 263286^2 + 370755^2 .

It is not a de Polignac number, because 206778787821 - 2³⁴ = 189598918637 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (206778787421) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 885826 + ... + 1094643.

It is an arithmetic number, because the mean of its divisors is an integer number (15456578115).

Almost surely, 2^206778787821 is an apocalyptic number.

It is an amenable number.

206778787821 is a deficient number, since it is larger than the sum of its proper divisors (102352774479).

206778787821 is a wasteful number, since it uses less digits than its factorization.

206778787821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1981770 (or 1981761 counting only the distinct ones).

The product of its (nonzero) digits is 29503488, while the sum is 63.

The spelling of 206778787821 in words is "two hundred six billion, seven hundred seventy-eight million, seven hundred eighty-seven thousand, eight hundred twenty-one".