721661671 has 4 divisors (see below), whose sum is σ = 724230144. Its totient is φ = 719093200.

The previous prime is 721661663. The next prime is 721661701. The reversal of 721661671 is 176166127.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 721661671 - 2³ = 721661663 is a prime.

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 721661671.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721661071) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 1283815 + ... + 1284376.

It is an arithmetic number, because the mean of its divisors is an integer number (181057536).

Almost surely, 2^721661671 is an apocalyptic number.

721661671 is a deficient number, since it is larger than the sum of its proper divisors (2568473).

721661671 is a wasteful number, since it uses less digits than its factorization.

721661671 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2568472.

The product of its digits is 21168, while the sum is 37.

The square root of 721661671 is about 26863.7612965869. The cubic root of 721661671 is about 896.9699214424.

It can be divided in two parts, 72166 and 1671, that added together give a palindrome (73837).

The spelling of 721661671 in words is "seven hundred twenty-one million, six hundred sixty-one thousand, six hundred seventy-one".