216391788 has 18 divisors (see below), whose sum is σ = 546990444. Its totient is φ = 72130584.

The previous prime is 216391757. The next prime is 216391789. The reversal of 216391788 is 887193612.

216391788 is a `hidden beast` number, since 2 + 1 + 639 + 1 + 7 + 8 + 8 = 666.

216391788 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a tau number, because it is divible by the number of its divisors (18).

It is not an unprimeable number, because it can be changed into a prime (216391789) 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, 3005406 + ... + 3005477.

It is an arithmetic number, because the mean of its divisors is an integer number (30388358).

Almost surely, 2^216391788 is an apocalyptic number.

It is an amenable number.

216391788 is an abundant number, since it is smaller than the sum of its proper divisors (330598656).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

216391788 is a wasteful number, since it uses less digits than its factorization.

216391788 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6010893 (or 6010888 counting only the distinct ones).

The product of its digits is 145152, while the sum is 45.

The square root of 216391788 is about 14710.2613165096. The cubic root of 216391788 is about 600.3625475547.

The spelling of 216391788 in words is "two hundred sixteen million, three hundred ninety-one thousand, seven hundred eighty-eight".