721987 has 4 divisors (see below), whose sum is σ = 825136. Its totient is φ = 618840.

The previous prime is 721979. The next prime is 721991. The reversal of 721987 is 789127.

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 721987 - 2³ = 721979 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (721997) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 51564 + ... + 51577.

It is an arithmetic number, because the mean of its divisors is an integer number (206284).

2⁷²¹⁹⁸⁷ is an apocalyptic number.

721987 is a deficient number, since it is larger than the sum of its proper divisors (103149).

721987 is a wasteful number, since it uses less digits than its factorization.

721987 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 103148.

The product of its digits is 7056, while the sum is 34.

The square root of 721987 is about 849.6981817092. The cubic root of 721987 is about 89.7104687497.

The spelling of 721987 in words is "seven hundred twenty-one thousand, nine hundred eighty-seven".