681521 has 2 divisors, whose sum is σ = 681522. Its totient is φ = 681520.

The previous prime is 681497. The next prime is 681523. The reversal of 681521 is 125186.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 579121 + 102400 = 761^2 + 320^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-681521 is a prime.

Together with 681523, it forms a pair of twin primes.

It is a Chen prime.

It is a nialpdrome in base 16.

It is not a weakly prime, because it can be changed into another prime (681523) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 340760 + 340761.

It is an arithmetic number, because the mean of its divisors is an integer number (340761).

2⁶⁸¹⁵²¹ is an apocalyptic number.

It is an amenable number.

681521 is a deficient number, since it is larger than the sum of its proper divisors (1).

681521 is an equidigital number, since it uses as much as digits as its factorization.

681521 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 480, while the sum is 23.

The square root of 681521 is about 825.5428517043. The cubic root of 681521 is about 88.0021091092.

The spelling of 681521 in words is "six hundred eighty-one thousand, five hundred twenty-one".