209887861 has 4 divisors (see below), whose sum is σ = 209917152. Its totient is φ = 209858572.

The previous prime is 209887849. The next prime is 209887879. The reversal of 209887861 is 168788902.

It is the 5915-th star number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 168788902 = 2 ⋅84394451.

It is a cyclic number.

It is not a de Polignac number, because 209887861 - 2¹⁹ = 209363573 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 (209887801) 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, 4110 + ... + 20896.

It is an arithmetic number, because the mean of its divisors is an integer number (52479288).

Almost surely, 2^209887861 is an apocalyptic number.

It is an amenable number.

209887861 is a deficient number, since it is larger than the sum of its proper divisors (29291).

209887861 is a wasteful number, since it uses less digits than its factorization.

209887861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29290.

The product of its (nonzero) digits is 387072, while the sum is 49.

The square root of 209887861 is about 14487.5070664349. The cubic root of 209887861 is about 594.2863755711.

The spelling of 209887861 in words is "two hundred nine million, eight hundred eighty-seven thousand, eight hundred sixty-one".