665642581 has 4 divisors (see below), whose sum is σ = 665894464. Its totient is φ = 665390700.

The previous prime is 665642573. The next prime is 665642647. The reversal of 665642581 is 185246566.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 665642581 - 2³ = 665642573 is a prime.

It is a super-2 number, since 2×665642581² = 886160091280683122, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (665642501) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 121935 + ... + 127276.

It is an arithmetic number, because the mean of its divisors is an integer number (166473616).

Almost surely, 2^665642581 is an apocalyptic number.

It is an amenable number.

665642581 is a deficient number, since it is larger than the sum of its proper divisors (251883).

665642581 is a wasteful number, since it uses less digits than its factorization.

665642581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 251882.

The product of its digits is 345600, while the sum is 43.

The square root of 665642581 is about 25800.0500193314. The cubic root of 665642581 is about 873.1329248821.

The spelling of 665642581 in words is "six hundred sixty-five million, six hundred forty-two thousand, five hundred eighty-one".