501661 has 4 divisors (see below), whose sum is σ = 504000. Its totient is φ = 499324.

The previous prime is 501659. The next prime is 501691. The reversal of 501661 is 166105.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 501661 - 2¹ = 501659 is a prime.

It is a Duffinian number.

501661 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (501601) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 811 + ... + 1288.

It is an arithmetic number, because the mean of its divisors is an integer number (126000).

2⁵⁰¹⁶⁶¹ is an apocalyptic number.

It is an amenable number.

501661 is a deficient number, since it is larger than the sum of its proper divisors (2339).

501661 is a wasteful number, since it uses less digits than its factorization.

501661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2338.

The product of its (nonzero) digits is 180, while the sum is 19.

The square root of 501661 is about 708.2803117411. The cubic root of 501661 is about 79.4578445600.

Adding to 501661 its reverse (166105), we get a palindrome (667766).

It can be divided in two parts, 50 and 1661, that added together give a triangular number (1711 = T₅₈).

The spelling of 501661 in words is "five hundred one thousand, six hundred sixty-one".