206809781 has 4 divisors (see below), whose sum is σ = 211853964. Its totient is φ = 201765600.

The previous prime is 206809753. The next prime is 206809783. The reversal of 206809781 is 187908602.

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 72829156 + 133980625 = 8534^2 + 11575^2 .

It is a cyclic number.

It is not a de Polignac number, because 206809781 - 2²² = 202615477 is a prime.

It is a super-2 number, since 2×206809781² = 85540571034535922, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (41), and also a Moran number because the ratio is a prime number: 5044141 = 206809781 / (2 + 0 + 6 + 8 + 0 + 9 + 7 + 8 + 1).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (206809783) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2522030 + ... + 2522111.

It is an arithmetic number, because the mean of its divisors is an integer number (52963491).

Almost surely, 2^206809781 is an apocalyptic number.

It is an amenable number.

206809781 is a deficient number, since it is larger than the sum of its proper divisors (5044183).

206809781 is an equidigital number, since it uses as much as digits as its factorization.

206809781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5044182.

The product of its (nonzero) digits is 48384, while the sum is 41.

The square root of 206809781 is about 14380.8824833527. The cubic root of 206809781 is about 591.3669168522.

The spelling of 206809781 in words is "two hundred six million, eight hundred nine thousand, seven hundred eighty-one".