216240021 has 12 divisors (see below), whose sum is σ = 317009472. Its totient is φ = 142007976.

The previous prime is 216239999. The next prime is 216240023. The reversal of 216240021 is 120042612.

216240021 is a `hidden beast` number, since 21 + 624 + 0 + 0 + 21 = 666.

It is not a de Polignac number, because 216240021 - 2⁶ = 216239957 is a prime.

It is a super-3 number, since 3×216240021³ (a number of 26 digits) contains 333 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 216239976 and 216240003.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (216240023) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 178701 + ... + 179906.

It is an arithmetic number, because the mean of its divisors is an integer number (26417456).

Almost surely, 2^216240021 is an apocalyptic number.

It is an amenable number.

216240021 is a deficient number, since it is larger than the sum of its proper divisors (100769451).

216240021 is a wasteful number, since it uses less digits than its factorization.

216240021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 358680 (or 358677 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 18.

The square root of 216240021 is about 14705.1018697594. The cubic root of 216240021 is about 600.2221593985. Note that the first 3 decimals are identical.

Adding to 216240021 its reverse (120042612), we get a palindrome (336282633).

The spelling of 216240021 in words is "two hundred sixteen million, two hundred forty thousand, twenty-one".