6781 has 2 divisors, whose sum is σ = 6782. Its totient is φ = 6780.

The previous prime is 6779. The next prime is 6791. The reversal of 6781 is 1876.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 5625 + 1156 = 75^2 + 34^2 .

It is a cyclic number.

It is not a de Polignac number, because 6781 - 2¹ = 6779 is a prime.

It is a super-2 number, since 2×6781² = 91963922, which contains 22 as substring.

Together with 6779, it forms a pair of twin primes.

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

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (6701) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3390 + 3391.

It is an arithmetic number, because the mean of its divisors is an integer number (3391).

2⁶⁷⁸¹ is an apocalyptic number.

It is an amenable number.

6781 is a deficient number, since it is larger than the sum of its proper divisors (1).

6781 is an equidigital number, since it uses as much as digits as its factorization.

6781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 336, while the sum is 22.

The square root of 6781 is about 82.3468275042. The cubic root of 6781 is about 18.9277030913.

Adding to 6781 its product of digits (336), we get a palindrome (7117).

It can be divided in two parts, 6 and 781, that added together give a palindrome (787).

The spelling of 6781 in words is "six thousand, seven hundred eighty-one".