217881423781 has 6 divisors (see below), whose sum is σ = 253453901190. Its totient is φ = 186755506056.

The previous prime is 217881423743. The next prime is 217881423803. The reversal of 217881423781 is 187324188712.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 206305815681 + 11575608100 = 454209^2 + 107590^2 .

It is not a de Polignac number, because 217881423781 - 2¹¹ = 217881421733 is a prime.

It is a super-2 number, since 2×217881423781² (a number of 23 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (217881423481) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 2223279786 + ... + 2223279883.

It is an arithmetic number, because the mean of its divisors is an integer number (42242316865).

Almost surely, 2^217881423781 is an apocalyptic number.

It is an amenable number.

217881423781 is a deficient number, since it is larger than the sum of its proper divisors (35572477409).

217881423781 is an equidigital number, since it uses as much as digits as its factorization.

217881423781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4446559683 (or 4446559676 counting only the distinct ones).

The product of its digits is 1204224, while the sum is 52.

The spelling of 217881423781 in words is "two hundred seventeen billion, eight hundred eighty-one million, four hundred twenty-three thousand, seven hundred eighty-one".