1665 has 12 divisors (see below), whose sum is σ = 2964. Its totient is φ = 864.

The previous prime is 1663. The next prime is 1667. The reversal of 1665 is 5661.

1665 is a *`hidden beast`* number, since 1 + 665 = 666.

It is an interprime number because it is at equal distance from previous prime (1663) and next prime (1667).

It can be written as a sum of positive squares in 2 ways, for example, as 1089 + 576 = 33^2 + 24^2 .

It is not a de Polignac number, because 1665 - 2^{1} = 1663 is a prime.

It is a hoax number, since the sum of its digits (18) coincides with the sum of the digits of its distinct prime factors.

Its product of digits (180) is a multiple of the sum of its prime divisors (45).

It is a Curzon number.

It is a plaindrome in base 7.

It is a nialpdrome in base 15.

It is not an unprimeable number, because it can be changed into a prime (1663) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 27 + ... + 63.

It is an arithmetic number, because the mean of its divisors is an integer number (247).

It is a Proth number, since it is equal to 13 ⋅ 2^{7} + 1 and 13 < 2^{7}.

2^{1665} is an apocalyptic number.

1665 is a gapful number since it is divisible by the number (15) formed by its first and last digit.

It is an amenable number.

1665 is a deficient number, since it is larger than the sum of its proper divisors (1299).

1665 is a wasteful number, since it uses less digits than its factorization.

1665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 48 (or 45 counting only the distinct ones).

The product of its digits is 180, while the sum is 18.

The square root of 1665 is about 40.8044115262. The cubic root of 1665 is about 11.8523575932.

Subtracting from 1665 its product of digits (180), we obtain a triangular number (1485 = T_{54}).

It can be divided in two parts, 166 and 5, that added together give a palindrome (171).

The spelling of 1665 in words is "one thousand, six hundred sixty-five".

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