666499721 has 16 divisors (see below), whose sum is σ = 713448960. Its totient is φ = 621250560.

The previous prime is 666499679. The next prime is 666499741. The reversal of 666499721 is 127994666.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-666499721 is a prime.

It is a super-3 number, since 3×666499721³ (a number of 27 digits) contains 333 as substring.

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 666499721.

It is not an unprimeable number, because it can be changed into a prime (666499741) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 577481 + ... + 578633.

It is an arithmetic number, because the mean of its divisors is an integer number (44590560).

Almost surely, 2^666499721 is an apocalyptic number.

It is an amenable number.

666499721 is a deficient number, since it is larger than the sum of its proper divisors (46949239).

666499721 is a wasteful number, since it uses less digits than its factorization.

666499721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1856.

The product of its digits is 979776, while the sum is 50.

The square root of 666499721 is about 25816.6558833634. The cubic root of 666499721 is about 873.5075384121.

The spelling of 666499721 in words is "six hundred sixty-six million, four hundred ninety-nine thousand, seven hundred twenty-one".