661765 has 8 divisors (see below), whose sum is σ = 855288. Its totient is φ = 488640.

The previous prime is 661741. The next prime is 661769. The reversal of 661765 is 567166.

It can be written as a sum of positive squares in 4 ways, for example, as 20164 + 641601 = 142^2 + 801^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 661765 - 2⁹ = 661253 is a prime.

It is a Duffinian number.

661765 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661769) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5026 + ... + 5155.

It is an arithmetic number, because the mean of its divisors is an integer number (106911).

2⁶⁶¹⁷⁶⁵ is an apocalyptic number.

661765 is a gapful number since it is divisible by the number (65) formed by its first and last digit.

It is an amenable number.

661765 is a deficient number, since it is larger than the sum of its proper divisors (193523).

661765 is a wasteful number, since it uses less digits than its factorization.

661765 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10199.

The product of its digits is 7560, while the sum is 31.

The square root of 661765 is about 813.4893975953. The cubic root of 661765 is about 87.1434195840.

The spelling of 661765 in words is "six hundred sixty-one thousand, seven hundred sixty-five".