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2781 = 33103
BaseRepresentation
bin101011011101
310211000
4223131
542111
620513
711052
oct5335
93730
102781
1120a9
121739
13135c
141029
15c56

2781 has 8 divisors (see below), whose sum is σ = 4160. Its totient is φ = 1836.

The previous prime is 2777. The next prime is 2789. The reversal of 2781 is 1872.

2781 is nontrivially palindromic in base 8.

It is not a de Polignac number, because 2781 - 22 = 2777 is a prime.

It is a super-2 number, since 2×27812 = 15467922, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

Its product of digits (112) is a multiple of the sum of its prime factors (112).

2781 is a modest number, since divided by 81 gives 27 as remainder.

It is a Curzon number.

2781 is a lucky number.

It is a plaindrome in base 13 and base 16.

It is a nialpdrome in base 5.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2789) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 25 + ... + 78.

It is an arithmetic number, because the mean of its divisors is an integer number (520).

It is an amenable number.

2781 is a deficient number, since it is larger than the sum of its proper divisors (1379).

2781 is a wasteful number, since it uses less digits than its factorization.

2781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 112 (or 106 counting only the distinct ones).

The product of its digits is 112, while the sum is 18.

The square root of 2781 is about 52.7351874937. The cubic root of 2781 is about 14.0626444430.

Subtracting from 2781 its reverse (1872), we obtain a palindrome (909).

It can be divided in two parts, 27 and 81, that multiplied together give a 7-th power (2187 = 37).

The spelling of 2781 in words is "two thousand, seven hundred eighty-one".

Divisors: 1 3 9 27 103 309 927 2781