216849781 has 4 divisors (see below), whose sum is σ = 216893772. Its totient is φ = 216805792.

The previous prime is 216849769. The next prime is 216849797. The reversal of 216849781 is 187948612.

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

It can be written as a sum of positive squares in 2 ways, for example, as 78411025 + 138438756 = 8855^2 + 11766^2 .

It is a cyclic number.

It is not a de Polignac number, because 216849781 - 2⁷ = 216849653 is a prime.

It is a super-2 number, since 2×216849781² = 94047655039495922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (216849761) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 13510 + ... + 24823.

It is an arithmetic number, because the mean of its divisors is an integer number (54223443).

Almost surely, 2^216849781 is an apocalyptic number.

It is an amenable number.

216849781 is a deficient number, since it is larger than the sum of its proper divisors (43991).

216849781 is an equidigital number, since it uses as much as digits as its factorization.

216849781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 43990.

The product of its digits is 193536, while the sum is 46.

The square root of 216849781 is about 14725.8202148471. The cubic root of 216849781 is about 600.7858046617.

The spelling of 216849781 in words is "two hundred sixteen million, eight hundred forty-nine thousand, seven hundred eighty-one".