218516991 has 16 divisors (see below), whose sum is σ = 363249408. Its totient is φ = 113515200.

The previous prime is 218516957. The next prime is 218516999. The reversal of 218516991 is 199615812.

It is not a de Polignac number, because 218516991 - 2¹³ = 218508799 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (218516999) 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 in 15 ways as a sum of consecutive naturals, for example, 472750 + ... + 473211.

It is an arithmetic number, because the mean of its divisors is an integer number (22703088).

Almost surely, 2^218516991 is an apocalyptic number.

218516991 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

218516991 is a deficient number, since it is larger than the sum of its proper divisors (144732417).

218516991 is a wasteful number, since it uses less digits than its factorization.

218516991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 945982.

The product of its digits is 38880, while the sum is 42.

The square root of 218516991 is about 14782.3202170701. The cubic root of 218516991 is about 602.3215529566.

The spelling of 218516991 in words is "two hundred eighteen million, five hundred sixteen thousand, nine hundred ninety-one".