218639861 has 6 divisors (see below), whose sum is σ = 240323286. Its totient is φ = 198763400.

The previous prime is 218639849. The next prime is 218639881. The reversal of 218639861 is 168936812.

218639861 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in only one way, i.e., 110355025 + 108284836 = 10505^2 + 10406^2 .

It is not a de Polignac number, because 218639861 - 2¹⁴ = 218623477 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 (218639881) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 903350 + ... + 903591.

It is an arithmetic number, because the mean of its divisors is an integer number (40053881).

Almost surely, 2^218639861 is an apocalyptic number.

It is an amenable number.

218639861 is a deficient number, since it is larger than the sum of its proper divisors (21683425).

218639861 is a wasteful number, since it uses less digits than its factorization.

218639861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1806963 (or 1806952 counting only the distinct ones).

The product of its digits is 124416, while the sum is 44.

The square root of 218639861 is about 14786.4756111793. The cubic root of 218639861 is about 602.4344250068.

The spelling of 218639861 in words is "two hundred eighteen million, six hundred thirty-nine thousand, eight hundred sixty-one".