665551 has 8 divisors (see below), whose sum is σ = 731520. Its totient is φ = 602712.

The previous prime is 665549. The next prime is 665557. The reversal of 665551 is 155566.

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 665551 - 2¹ = 665549 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a nialpdrome in base 10.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (665557) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 325 + ... + 1198.

It is an arithmetic number, because the mean of its divisors is an integer number (91440).

2⁶⁶⁵⁵⁵¹ is an apocalyptic number.

665551 is a deficient number, since it is larger than the sum of its proper divisors (65969).

665551 is a wasteful number, since it uses less digits than its factorization.

665551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1565.

The product of its digits is 4500, while the sum is 28.

The square root of 665551 is about 815.8130913389. The cubic root of 665551 is about 87.3092880342.

The spelling of 665551 in words is "six hundred sixty-five thousand, five hundred fifty-one".