218501981 has 4 divisors (see below), whose sum is σ = 225550464. Its totient is φ = 211453500.

The previous prime is 218501951. The next prime is 218501999. The reversal of 218501981 is 189105812.

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 218501981 - 2¹⁰ = 218500957 is a prime.

It is a super-2 number, since 2×218501981² = 95486231401848722, 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 (218501951) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3524195 + ... + 3524256.

It is an arithmetic number, because the mean of its divisors is an integer number (56387616).

Almost surely, 2^218501981 is an apocalyptic number.

It is an amenable number.

218501981 is a deficient number, since it is larger than the sum of its proper divisors (7048483).

218501981 is an equidigital number, since it uses as much as digits as its factorization.

218501981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7048482.

The product of its (nonzero) digits is 5760, while the sum is 35.

The square root of 218501981 is about 14781.8125072672. The cubic root of 218501981 is about 602.3077614226.

The spelling of 218501981 in words is "two hundred eighteen million, five hundred one thousand, nine hundred eighty-one".