721099665 has 80 divisors (see below), whose sum is σ = 1518745536. Its totient is φ = 322704000.

The previous prime is 721099651. The next prime is 721099679. The reversal of 721099665 is 566990127.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (721099651) and next prime (721099679).

It is not a de Polignac number, because 721099665 - 2⁷ = 721099537 is a prime.

It is a super-2 number, since 2×721099665² = 1039969453726224450, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a self number, because there is not a number n which added to its sum of digits gives 721099665.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 79 ways as a sum of consecutive naturals, for example, 51690 + ... + 64140.

Almost surely, 2^721099665 is an apocalyptic number.

It is an amenable number.

721099665 is an abundant number, since it is smaller than the sum of its proper divisors (797645871).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

721099665 is a wasteful number, since it uses less digits than its factorization.

721099665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12492 (or 12483 counting only the distinct ones).

The product of its (nonzero) digits is 204120, while the sum is 45.

The square root of 721099665 is about 26853.2989593458. The cubic root of 721099665 is about 896.7370175697.

The spelling of 721099665 in words is "seven hundred twenty-one million, ninety-nine thousand, six hundred sixty-five".