721513661 has 8 divisors (see below), whose sum is σ = 794748864. Its totient is φ = 649552320.

The previous prime is 721513633. The next prime is 721513691. The reversal of 721513661 is 166315127.

721513661 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 721513661 - 2²² = 717319357 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721513631) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 317276 + ... + 319541.

It is an arithmetic number, because the mean of its divisors is an integer number (99343608).

Almost surely, 2^721513661 is an apocalyptic number.

It is an amenable number.

721513661 is a deficient number, since it is larger than the sum of its proper divisors (73235203).

721513661 is a wasteful number, since it uses less digits than its factorization.

721513661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 636931.

The product of its digits is 7560, while the sum is 32.

The square root of 721513661 is about 26861.0063288776. The cubic root of 721513661 is about 896.9085955696.

Adding to 721513661 its reverse (166315127), we get a palindrome (887828788).

The spelling of 721513661 in words is "seven hundred twenty-one million, five hundred thirteen thousand, six hundred sixty-one".