216821866 has 4 divisors (see below), whose sum is σ = 325232802. Its totient is φ = 108410932.

The previous prime is 216821809. The next prime is 216821921. The reversal of 216821866 is 668128612.

216821866 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 159289641 + 57532225 = 12621^2 + 7585^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 54205465 + ... + 54205468.

Almost surely, 2^216821866 is an apocalyptic number.

216821866 is a deficient number, since it is larger than the sum of its proper divisors (108410936).

216821866 is a wasteful number, since it uses less digits than its factorization.

216821866 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 108410935.

The product of its digits is 55296, while the sum is 40.

The square root of 216821866 is about 14724.8723593789. The cubic root of 216821866 is about 600.7600239033.

The spelling of 216821866 in words is "two hundred sixteen million, eight hundred twenty-one thousand, eight hundred sixty-six".