721538 has 4 divisors (see below), whose sum is σ = 1082310. Its totient is φ = 360768.

The previous prime is 721529. The next prime is 721547. The reversal of 721538 is 835127.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 835127 = 37 ⋅22571.

It is an interprime number because it is at equal distance from previous prime (721529) and next prime (721547).

It can be written as a sum of positive squares in only one way, i.e., 644809 + 76729 = 803^2 + 277^2 .

It is an Ulam number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 721538.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 180383 + ... + 180386.

2⁷²¹⁵³⁸ is an apocalyptic number.

721538 is a deficient number, since it is larger than the sum of its proper divisors (360772).

721538 is a wasteful number, since it uses less digits than its factorization.

721538 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 360771.

The product of its digits is 1680, while the sum is 26.

The square root of 721538 is about 849.4339291552. The cubic root of 721538 is about 89.6918680670.

It can be divided in two parts, 7215 and 38, that multiplied together give a triangular number (274170 = T₇₄₀).

The spelling of 721538 in words is "seven hundred twenty-one thousand, five hundred thirty-eight".