211681 has 2 divisors, whose sum is σ = 211682. Its totient is φ = 211680.

The previous prime is 211663. The next prime is 211691. The reversal of 211681 is 186112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 211600 + 81 = 460^2 + 9^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-211681 is a prime.

It is a super-2 number, since 2×211681² = 89617691522, which contains 22 as substring.

211681 is a lucky number.

It is not a weakly prime, because it can be changed into another prime (211661) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 105840 + 105841.

It is an arithmetic number, because the mean of its divisors is an integer number (105841).

2²¹¹⁶⁸¹ is an apocalyptic number.

It is an amenable number.

211681 is a deficient number, since it is larger than the sum of its proper divisors (1).

211681 is an equidigital number, since it uses as much as digits as its factorization.

211681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 96, while the sum is 19.

The square root of 211681 is about 460.0880350542. The cubic root of 211681 is about 59.5973971507.

Adding to 211681 its reverse (186112), we get a palindrome (397793).

It can be divided in two parts, 2116 and 81, that multiplied together give a square (171396 = 414²).

The spelling of 211681 in words is "two hundred eleven thousand, six hundred eighty-one".