208939781 has 2 divisors, whose sum is σ = 208939782. Its totient is φ = 208939780.

The previous prime is 208939771. The next prime is 208939793. The reversal of 208939781 is 187939802.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 197824225 + 11115556 = 14065^2 + 3334^2 .

It is a cyclic number.

It is not a de Polignac number, because 208939781 - 2¹⁰ = 208938757 is a prime.

It is a super-2 number, since 2×208939781² = 87311664168655922, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (208939711) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 104469890 + 104469891.

It is an arithmetic number, because the mean of its divisors is an integer number (104469891).

Almost surely, 2^208939781 is an apocalyptic number.

It is an amenable number.

208939781 is a deficient number, since it is larger than the sum of its proper divisors (1).

208939781 is an equidigital number, since it uses as much as digits as its factorization.

208939781 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 217728, while the sum is 47.

The square root of 208939781 is about 14454.7494270914. The cubic root of 208939781 is about 593.3902120773.

The spelling of 208939781 in words is "two hundred eight million, nine hundred thirty-nine thousand, seven hundred eighty-one".