208139861 has 2 divisors, whose sum is σ = 208139862. Its totient is φ = 208139860.

The previous prime is 208139849. The next prime is 208139881. The reversal of 208139861 is 168931802.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 204661636 + 3478225 = 14306^2 + 1865^2 .

It is a cyclic number.

It is not a de Polignac number, because 208139861 - 2¹⁴ = 208123477 is a prime.

It is a Sophie Germain prime.

It is a Chen 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 (208139801) 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 as a sum of consecutive naturals, namely, 104069930 + 104069931.

It is an arithmetic number, because the mean of its divisors is an integer number (104069931).

Almost surely, 2^208139861 is an apocalyptic number.

It is an amenable number.

208139861 is a deficient number, since it is larger than the sum of its proper divisors (1).

208139861 is an equidigital number, since it uses as much as digits as its factorization.

208139861 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 20736, while the sum is 38.

The square root of 208139861 is about 14427.0530947938. The cubic root of 208139861 is about 592.6319844601.

The spelling of 208139861 in words is "two hundred eight million, one hundred thirty-nine thousand, eight hundred sixty-one".