669781 has 6 divisors (see below), whose sum is σ = 779190. Its totient is φ = 574056.

The previous prime is 669763. The next prime is 669787. The reversal of 669781 is 187966.

It can be written as a sum of positive squares in only one way, i.e., 625681 + 44100 = 791^2 + 210^2 .

It is not a de Polignac number, because 669781 - 2¹⁷ = 538709 is a prime.

It is a super-2 number, since 2×669781² = 897213175922, which contains 22 as substring.

It is an Ulam number.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 669781.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (669787) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 6786 + ... + 6883.

It is an arithmetic number, because the mean of its divisors is an integer number (129865).

2⁶⁶⁹⁷⁸¹ is an apocalyptic number.

It is an amenable number.

669781 is a deficient number, since it is larger than the sum of its proper divisors (109409).

669781 is a wasteful number, since it uses less digits than its factorization.

669781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13683 (or 13676 counting only the distinct ones).

The product of its digits is 18144, while the sum is 37.

The square root of 669781 is about 818.4014907122. The cubic root of 669781 is about 87.4938662367.

It can be divided in two parts, 66 and 9781, that multiplied together give a palindrome (645546).

The spelling of 669781 in words is "six hundred sixty-nine thousand, seven hundred eighty-one".