665651 has 4 divisors (see below), whose sum is σ = 760752. Its totient is φ = 570552.

The previous prime is 665633. The next prime is 665659. The reversal of 665651 is 156566.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 156566 = 2 ⋅78283.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-665651 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (665659) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 47540 + ... + 47553.

It is an arithmetic number, because the mean of its divisors is an integer number (190188).

2⁶⁶⁵⁶⁵¹ is an apocalyptic number.

665651 is a deficient number, since it is larger than the sum of its proper divisors (95101).

665651 is an equidigital number, since it uses as much as digits as its factorization.

665651 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 95100.

The product of its digits is 5400, while the sum is 29.

The square root of 665651 is about 815.8743775852. The cubic root of 665651 is about 87.3136605974.

It can be divided in two parts, 66565 and 1, that added together give a palindrome (66566).

The spelling of 665651 in words is "six hundred sixty-five thousand, six hundred fifty-one".