665617521 has 4 divisors (see below), whose sum is σ = 887490032. Its totient is φ = 443745012.

The previous prime is 665617489. The next prime is 665617529. The reversal of 665617521 is 125716566.

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 not a de Polignac number, because 665617521 - 2⁵ = 665617489 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 665617521.

It is not an unprimeable number, because it can be changed into a prime (665617529) 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, 110936251 + ... + 110936256.

It is an arithmetic number, because the mean of its divisors is an integer number (221872508).

Almost surely, 2^665617521 is an apocalyptic number.

It is an amenable number.

665617521 is a deficient number, since it is larger than the sum of its proper divisors (221872511).

665617521 is a wasteful number, since it uses less digits than its factorization.

665617521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 221872510.

The product of its digits is 75600, while the sum is 39.

The square root of 665617521 is about 25799.5643567871. The cubic root of 665617521 is about 873.1219675574.

The spelling of 665617521 in words is "six hundred sixty-five million, six hundred seventeen thousand, five hundred twenty-one".