2166781 has 4 divisors (see below), whose sum is σ = 2202364. Its totient is φ = 2131200.

The previous prime is 2166763. The next prime is 2166797. The reversal of 2166781 is 1876612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 864900 + 1301881 = 930^2 + 1141^2 .

It is a cyclic number.

It is not a de Polignac number, because 2166781 - 2¹³ = 2158589 is a prime.

It is a super-2 number, since 2×2166781² = 9389879803922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2166721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 17700 + ... + 17821.

It is an arithmetic number, because the mean of its divisors is an integer number (550591).

2^2166781 is an apocalyptic number.

It is an amenable number.

2166781 is a deficient number, since it is larger than the sum of its proper divisors (35583).

2166781 is an equidigital number, since it uses as much as digits as its factorization.

2166781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 35582.

The product of its digits is 4032, while the sum is 31.

The square root of 2166781 is about 1471.9989809779. The cubic root of 2166781 is about 129.4012106650.

The spelling of 2166781 in words is "two million, one hundred sixty-six thousand, seven hundred eighty-one".