217681 has 2 divisors, whose sum is σ = 217682. Its totient is φ = 217680.

The previous prime is 217667. The next prime is 217687. The reversal of 217681 is 186712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 147456 + 70225 = 384^2 + 265^2 .

It is a cyclic number.

It is not a de Polignac number, because 217681 - 2⁹ = 217169 is a prime.

It is a super-2 number, since 2×217681² = 94770035522, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (217687) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108840 + 108841.

It is an arithmetic number, because the mean of its divisors is an integer number (108841).

2²¹⁷⁶⁸¹ is an apocalyptic number.

It is an amenable number.

217681 is a deficient number, since it is larger than the sum of its proper divisors (1).

217681 is an equidigital number, since it uses as much as digits as its factorization.

217681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 672, while the sum is 25.

The square root of 217681 is about 466.5629646682. The cubic root of 217681 is about 60.1552461124.

It can be divided in two parts, 217 and 681, that added together give a palindrome (898).

The spelling of 217681 in words is "two hundred seventeen thousand, six hundred eighty-one".