2155781 has 2 divisors, whose sum is σ = 2155782. Its totient is φ = 2155780.

The previous prime is 2155733. The next prime is 2155793. The reversal of 2155781 is 1875512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1934881 + 220900 = 1391^2 + 470^2 .

It is a cyclic number.

It is not a de Polignac number, because 2155781 - 2⁶ = 2155717 is a prime.

It is a super-2 number, since 2×2155781² = 9294783439922, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (2155711) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1077890 + 1077891.

It is an arithmetic number, because the mean of its divisors is an integer number (1077891).

2^2155781 is an apocalyptic number.

It is an amenable number.

2155781 is a deficient number, since it is larger than the sum of its proper divisors (1).

2155781 is an equidigital number, since it uses as much as digits as its factorization.

2155781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2800, while the sum is 29.

The square root of 2155781 is about 1468.2578111490. The cubic root of 2155781 is about 129.1818639536.

The spelling of 2155781 in words is "two million, one hundred fifty-five thousand, seven hundred eighty-one".