781681 has 2 divisors, whose sum is σ = 781682. Its totient is φ = 781680.

The previous prime is 781673. The next prime is 781721. The reversal of 781681 is 186187.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 781456 + 225 = 884^2 + 15^2 .

It is an emirp because it is prime and its reverse (186187) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 781681 - 2³ = 781673 is a prime.

It is a super-2 number, since 2×781681² = 1222050371522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (781601) 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 as a sum of consecutive naturals, namely, 390840 + 390841.

It is an arithmetic number, because the mean of its divisors is an integer number (390841).

2⁷⁸¹⁶⁸¹ is an apocalyptic number.

It is an amenable number.

781681 is a deficient number, since it is larger than the sum of its proper divisors (1).

781681 is an equidigital number, since it uses as much as digits as its factorization.

781681 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 781681 is about 884.1272532843. The cubic root of 781681 is about 92.1177210732.

The spelling of 781681 in words is "seven hundred eighty-one thousand, six hundred eighty-one".