1645 has 8 divisors (see below), whose sum is σ = 2304. Its totient is φ = 1104.

The previous prime is 1637. The next prime is 1657. The reversal of 1645 is 5461.

Adding to 1645 its sum of digits (16), we get a palindrome (1661).

It can be divided in two parts, 164 and 5, that multiplied together give a triangular number (820 = T_{40}).

1645 = 8^{2} + 9^{2} + ... + 17^{2}.

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

It is a cyclic number.

It is not a de Polignac number, because 1645 - 2^{3} = 1637 is a prime.

It is a super-3 number, since 3×1645^{3} = 13354233375, which contains 333 as substring.

It is a Duffinian number.

1645 is a lucky number.

It is a plaindrome in base 9, base 11 and base 16.

It is a nialpdrome in base 12 and base 13.

It is a congruent number.

It is an unprimeable number.

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, 12 + ... + 58.

It is an arithmetic number, because the mean of its divisors is an integer number (288).

It is an amenable number.

1645 is a deficient number, since it is larger than the sum of its proper divisors (659).

1645 is an equidigital number, since it uses as much as digits as its factorization.

1645 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 59.

The product of its digits is 120, while the sum is 16.

The square root of 1645 is about 40.5585995813. The cubic root of 1645 is about 11.8047094101.

The spelling of 1645 in words is "one thousand, six hundred forty-five".

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