665820 has 72 divisors (see below), whose sum is σ = 2109744. Its totient is φ = 176256.

The previous prime is 665813. The next prime is 665843. The reversal of 665820 is 28566.

665820 = 109² + 110² + ... + 148².

665820 is a `hidden beast` number, since 6 + 658 + 2 + 0 = 666.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a nialpdrome in base 7.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 4792 + ... + 4928.

It is an arithmetic number, because the mean of its divisors is an integer number (29302).

2⁶⁶⁵⁸²⁰ is an apocalyptic number.

665820 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 665820, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1054872).

665820 is an abundant number, since it is smaller than the sum of its proper divisors (1443924).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

665820 is a wasteful number, since it uses less digits than its factorization.

665820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 161 (or 147 counting only the distinct ones).

The product of its (nonzero) digits is 2880, while the sum is 27.

The square root of 665820 is about 815.9779408783. The cubic root of 665820 is about 87.3210492340.

It can be divided in two parts, 665 and 820, that added together give a triangular number (1485 = T₅₄).

The spelling of 665820 in words is "six hundred sixty-five thousand, eight hundred twenty".