216553781 has 4 divisors (see below), whose sum is σ = 217988064. Its totient is φ = 215119500.

The previous prime is 216553751. The next prime is 216553783. The reversal of 216553781 is 187355612.

216553781 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 216553781 - 2¹⁰ = 216552757 is a prime.

It is a super-2 number, since 2×216553781² = 93791080130791922, 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 (216553783) 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, 716915 + ... + 717216.

It is an arithmetic number, because the mean of its divisors is an integer number (54497016).

Almost surely, 2^216553781 is an apocalyptic number.

It is an amenable number.

216553781 is a deficient number, since it is larger than the sum of its proper divisors (1434283).

216553781 is a wasteful number, since it uses less digits than its factorization.

216553781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1434282.

The product of its digits is 50400, while the sum is 38.

The square root of 216553781 is about 14715.7664088555. The cubic root of 216553781 is about 600.5123226033.

The spelling of 216553781 in words is "two hundred sixteen million, five hundred fifty-three thousand, seven hundred eighty-one".