217306857781 has 8 divisors (see below), whose sum is σ = 234043470360. Its totient is φ = 200573202432.

The previous prime is 217306857769. The next prime is 217306857787. The reversal of 217306857781 is 187758603712.

217306857781 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 4 ways, for example, as 887444100 + 216419413681 = 29790^2 + 465209^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 217306857781 - 2⁵ = 217306857749 is a prime.

It is a super-3 number, since 3×217306857781³ (a number of 35 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (217306857787) 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 7 ways as a sum of consecutive naturals, for example, 585496 + ... + 881713.

It is an arithmetic number, because the mean of its divisors is an integer number (29255433795).

Almost surely, 2^217306857781 is an apocalyptic number.

It is an amenable number.

217306857781 is a deficient number, since it is larger than the sum of its proper divisors (16736612579).

217306857781 is a wasteful number, since it uses less digits than its factorization.

217306857781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1478615.

The product of its (nonzero) digits is 3951360, while the sum is 55.

The spelling of 217306857781 in words is "two hundred seventeen billion, three hundred six million, eight hundred fifty-seven thousand, seven hundred eighty-one".