216921890 has 16 divisors (see below), whose sum is σ = 390674232. Its totient is φ = 86721024.

The previous prime is 216921889. The next prime is 216921893. The reversal of 216921890 is 98129612.

It can be written as a sum of positive squares in 4 ways, for example, as 163763209 + 53158681 = 12797^2 + 7291^2 .

It is a super-2 number, since 2×216921890² = 94110212722344200, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is not an unprimeable number, because it can be changed into a prime (216921893) 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 7 ways as a sum of consecutive naturals, for example, 17522 + ... + 27218.

Almost surely, 2^216921890 is an apocalyptic number.

216921890 is a deficient number, since it is larger than the sum of its proper divisors (173752342).

216921890 is a wasteful number, since it uses less digits than its factorization.

216921890 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11941.

The product of its (nonzero) digits is 15552, while the sum is 38.

The square root of 216921890 is about 14728.2683978803. The cubic root of 216921890 is about 600.8523903296.

The spelling of 216921890 in words is "two hundred sixteen million, nine hundred twenty-one thousand, eight hundred ninety".