669966521 has 4 divisors (see below), whose sum is σ = 765676032. Its totient is φ = 574257012.

The previous prime is 669966509. The next prime is 669966523. The reversal of 669966521 is 125669966.

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, and also an emirpimes, since its reverse is a distinct semiprime: 125669966 = 2 ⋅62834983.

It is a de Polignac number, because none of the positive numbers 2^k-669966521 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 669966521.

It is not an unprimeable number, because it can be changed into a prime (669966523) 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, 47854745 + ... + 47854758.

It is an arithmetic number, because the mean of its divisors is an integer number (191419008).

Almost surely, 2^669966521 is an apocalyptic number.

It is an amenable number.

669966521 is a deficient number, since it is larger than the sum of its proper divisors (95709511).

669966521 is an equidigital number, since it uses as much as digits as its factorization.

669966521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 95709510.

The product of its digits is 1049760, while the sum is 50.

The square root of 669966521 is about 25883.7114997058. The cubic root of 669966521 is about 875.0194372825.

The spelling of 669966521 in words is "six hundred sixty-nine million, nine hundred sixty-six thousand, five hundred twenty-one".