689981 has 2 divisors, whose sum is σ = 689982. Its totient is φ = 689980.

The previous prime is 689963. The next prime is 689987. The reversal of 689981 is 189986.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 448900 + 241081 = 670^2 + 491^2 .

It is a cyclic number.

It is not a de Polignac number, because 689981 - 2⁶ = 689917 is a prime.

It is a super-2 number, since 2×689981² = 952147560722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (689987) 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, 344990 + 344991.

It is an arithmetic number, because the mean of its divisors is an integer number (344991).

2⁶⁸⁹⁹⁸¹ is an apocalyptic number.

It is an amenable number.

689981 is a deficient number, since it is larger than the sum of its proper divisors (1).

689981 is an equidigital number, since it uses as much as digits as its factorization.

689981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 31104, while the sum is 41.

The square root of 689981 is about 830.6509495570. The cubic root of 689981 is about 88.3647481317.

The spelling of 689981 in words is "six hundred eighty-nine thousand, nine hundred eighty-one".