216921921 has 8 divisors (see below), whose sum is σ = 306242784. Its totient is φ = 136107840.

The previous prime is 216921899. The next prime is 216921941. The reversal of 216921921 is 129129612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 216921921 - 2⁵ = 216921889 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (216921941) 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, 2126635 + ... + 2126736.

It is an arithmetic number, because the mean of its divisors is an integer number (38280348).

Almost surely, 2^216921921 is an apocalyptic number.

It is an amenable number.

216921921 is a deficient number, since it is larger than the sum of its proper divisors (89320863).

216921921 is a wasteful number, since it uses less digits than its factorization.

216921921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4253391.

The product of its digits is 3888, while the sum is 33.

The square root of 216921921 is about 14728.2694502783. The cubic root of 216921921 is about 600.8524189519.

It can be divided in two parts, 2169 and 21921, that added together give a triangular number (24090 = T₂₁₉).

The spelling of 216921921 in words is "two hundred sixteen million, nine hundred twenty-one thousand, nine hundred twenty-one".