211681661 has 2 divisors, whose sum is σ = 211681662. Its totient is φ = 211681660.

The previous prime is 211681633. The next prime is 211681667. The reversal of 211681661 is 166186112.

211681661 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 136165561 + 75516100 = 11669^2 + 8690^2 .

It is a cyclic number.

It is not a de Polignac number, because 211681661 - 2¹⁴ = 211665277 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (211681667) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 105840830 + 105840831.

It is an arithmetic number, because the mean of its divisors is an integer number (105840831).

Almost surely, 2^211681661 is an apocalyptic number.

It is an amenable number.

211681661 is a deficient number, since it is larger than the sum of its proper divisors (1).

211681661 is an equidigital number, since it uses as much as digits as its factorization.

211681661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3456, while the sum is 32.

The square root of 211681661 is about 14549.2838655378. The cubic root of 211681661 is about 595.9745918406.

The spelling of 211681661 in words is "two hundred eleven million, six hundred eighty-one thousand, six hundred sixty-one".