501720561 has 20 divisors (see below), whose sum is σ = 775331700. Its totient is φ = 322945056.

The previous prime is 501720559. The next prime is 501720563. The reversal of 501720561 is 165027105.

It is an interprime number because it is at equal distance from previous prime (501720559) and next prime (501720563).

It can be written as a sum of positive squares in 2 ways, for example, as 304851600 + 196868961 = 17460^2 + 14031^2 .

It is not a de Polignac number, because 501720561 - 2¹ = 501720559 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (501720563) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 104446 + ... + 109143.

It is an arithmetic number, because the mean of its divisors is an integer number (38766585).

Almost surely, 2^501720561 is an apocalyptic number.

It is an amenable number.

501720561 is a deficient number, since it is larger than the sum of its proper divisors (273611139).

501720561 is a wasteful number, since it uses less digits than its factorization.

501720561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 213630 (or 213621 counting only the distinct ones).

The product of its (nonzero) digits is 2100, while the sum is 27.

The square root of 501720561 is about 22399.1196478790. The cubic root of 501720561 is about 794.6098904828.

Adding to 501720561 its reverse (165027105), we get a palindrome (666747666).

The spelling of 501720561 in words is "five hundred one million, seven hundred twenty thousand, five hundred sixty-one".