216818581 has 18 divisors (see below), whose sum is σ = 255810870. Its totient is φ = 183233232.

The previous prime is 216818531. The next prime is 216818597. The reversal of 216818581 is 185818612.

It can be written as a sum of positive squares in only one way, i.e., 148011556 + 68807025 = 12166^2 + 8295^2 .

It is not a de Polignac number, because 216818581 - 2⁷ = 216818453 is a prime.

It is a super-2 number, since 2×216818581² = 94020594133707122, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (216818501) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 305455 + ... + 306163.

It is an arithmetic number, because the mean of its divisors is an integer number (14211715).

Almost surely, 2^216818581 is an apocalyptic number.

It is an amenable number.

216818581 is a deficient number, since it is larger than the sum of its proper divisors (38992289).

216818581 is an frugal number, since it uses more digits than its factorization.

216818581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 881 (or 795 counting only the distinct ones).

The product of its digits is 30720, while the sum is 40.

The square root of 216818581 is about 14724.7608129979. The cubic root of 216818581 is about 600.7569899125.

The spelling of 216818581 in words is "two hundred sixteen million, eight hundred eighteen thousand, five hundred eighty-one".