218171981 has 4 divisors (see below), whose sum is σ = 223245792. Its totient is φ = 213098172.

The previous prime is 218171977. The next prime is 218171983. The reversal of 218171981 is 189171812.

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.

It is a cyclic number.

It is not a de Polignac number, because 218171981 - 2² = 218171977 is a prime.

It is a super-2 number, since 2×218171981² = 95198026586928722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (218171983) 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, 2536841 + ... + 2536926.

It is an arithmetic number, because the mean of its divisors is an integer number (55811448).

Almost surely, 2^218171981 is an apocalyptic number.

It is an amenable number.

218171981 is a deficient number, since it is larger than the sum of its proper divisors (5073811).

218171981 is an equidigital number, since it uses as much as digits as its factorization.

218171981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5073810.

The product of its digits is 8064, while the sum is 38.

The square root of 218171981 is about 14770.6459235878. The cubic root of 218171981 is about 602.0043900961.

The spelling of 218171981 in words is "two hundred eighteen million, one hundred seventy-one thousand, nine hundred eighty-one".