216921931 has 4 divisors (see below), whose sum is σ = 217822264. Its totient is φ = 216021600.

The previous prime is 216921899. The next prime is 216921941. The reversal of 216921931 is 139129612.

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

It is a cyclic number.

It is not a de Polignac number, because 216921931 - 2⁵ = 216921899 is a prime.

It is a super-2 number, since 2×216921931² = 94110248297537522, which contains 22 as substring.

It is a Duffinian 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 (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 449805 + ... + 450286.

It is an arithmetic number, because the mean of its divisors is an integer number (54455566).

Almost surely, 2^216921931 is an apocalyptic number.

216921931 is a deficient number, since it is larger than the sum of its proper divisors (900333).

216921931 is an equidigital number, since it uses as much as digits as its factorization.

216921931 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 900332.

The product of its digits is 5832, while the sum is 34.

The square root of 216921931 is about 14728.2697897615. The cubic root of 216921931 is about 600.8524281849.

The spelling of 216921931 in words is "two hundred sixteen million, nine hundred twenty-one thousand, nine hundred thirty-one".