201781 has 2 divisors, whose sum is σ = 201782. Its totient is φ = 201780.

The previous prime is 201769. The next prime is 201787. The reversal of 201781 is 187102.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 128881 + 72900 = 359^2 + 270^2 .

It is a cyclic number.

It is not a de Polignac number, because 201781 - 2⁷ = 201653 is a prime.

It is a super-2 number, since 2×201781² = 81431143922, which contains 22 as substring.

It is a Chen prime.

It is an Ulam number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (201787) by changing a digit.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 100890 + 100891.

It is an arithmetic number, because the mean of its divisors is an integer number (100891).

2²⁰¹⁷⁸¹ is an apocalyptic number.

It is an amenable number.

201781 is a deficient number, since it is larger than the sum of its proper divisors (1).

201781 is an equidigital number, since it uses as much as digits as its factorization.

201781 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 112, while the sum is 19.

The square root of 201781 is about 449.2004007122. The cubic root of 201781 is about 58.6534312142.

Adding to 201781 its reverse (187102), we get a palindrome (388883).

The spelling of 201781 in words is "two hundred one thousand, seven hundred eighty-one".