681781 has 2 divisors, whose sum is σ = 681782. Its totient is φ = 681780.

The previous prime is 681773. The next prime is 681787. The reversal of 681781 is 187186.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 680625 + 1156 = 825^2 + 34^2 .

It is a cyclic number.

It is not a de Polignac number, because 681781 - 2³ = 681773 is a prime.

It is a super-2 number, since 2×681781² = 929650663922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (681787) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 340890 + 340891.

It is an arithmetic number, because the mean of its divisors is an integer number (340891).

2⁶⁸¹⁷⁸¹ is an apocalyptic number.

It is an amenable number.

681781 is a deficient number, since it is larger than the sum of its proper divisors (1).

681781 is an equidigital number, since it uses as much as digits as its factorization.

681781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2688, while the sum is 31.

The square root of 681781 is about 825.7003088288. The cubic root of 681781 is about 88.0132986100.

It can be divided in two parts, 68 and 1781, that added together give a square (1849 = 43²).

The spelling of 681781 in words is "six hundred eighty-one thousand, seven hundred eighty-one".