666733521 has 4 divisors (see below), whose sum is σ = 888978032. Its totient is φ = 444489012.

The previous prime is 666733517. The next prime is 666733531. The reversal of 666733521 is 125337666.

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 666733521 - 2² = 666733517 is a prime.

It is a super-3 number, since 3×666733521³ (a number of 27 digits) contains 333 as substring.

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 666733521.

It is not an unprimeable number, because it can be changed into a prime (666733511) 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, 111122251 + ... + 111122256.

It is an arithmetic number, because the mean of its divisors is an integer number (222244508).

Almost surely, 2^666733521 is an apocalyptic number.

It is an amenable number.

666733521 is a deficient number, since it is larger than the sum of its proper divisors (222244511).

666733521 is a wasteful number, since it uses less digits than its factorization.

666733521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 222244510.

The product of its digits is 136080, while the sum is 39.

The square root of 666733521 is about 25821.1835708590. The cubic root of 666733521 is about 873.6096650800.

The spelling of 666733521 in words is "six hundred sixty-six million, seven hundred thirty-three thousand, five hundred twenty-one".