666356051521 has 4 divisors (see below), whose sum is σ = 666360446512. Its totient is φ = 666351656532.

The previous prime is 666356051519. The next prime is 666356051533. The reversal of 666356051521 is 125150653666.

666356051521 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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: 125150653666 = 2 ⋅62575326833.

It is a cyclic number.

It is not a de Polignac number, because 666356051521 - 2¹ = 666356051519 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (666356058521) 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, 1961631 + ... + 2276116.

It is an arithmetic number, because the mean of its divisors is an integer number (166590111628).

Almost surely, 2^666356051521 is an apocalyptic number.

It is an amenable number.

666356051521 is a deficient number, since it is larger than the sum of its proper divisors (4394991).

666356051521 is a wasteful number, since it uses less digits than its factorization.

666356051521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4394990.

The product of its (nonzero) digits is 972000, while the sum is 46.

The spelling of 666356051521 in words is "six hundred sixty-six billion, three hundred fifty-six million, fifty-one thousand, five hundred twenty-one".