661331 has 8 divisors (see below), whose sum is σ = 734400. Its totient is φ = 590440.

The previous prime is 661327. The next prime is 661343. The reversal of 661331 is 133166.

661331 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 661331 - 2² = 661327 is a prime.

It is a super-2 number, since 2×661331² = 874717383122, which contains 22 as substring.

It is an Ulam number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (661321) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 140 + ... + 1158.

It is an arithmetic number, because the mean of its divisors is an integer number (91800).

2⁶⁶¹³³¹ is an apocalyptic number.

661331 is a deficient number, since it is larger than the sum of its proper divisors (73069).

661331 is a wasteful number, since it uses less digits than its factorization.

661331 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1089.

The product of its digits is 324, while the sum is 20.

The square root of 661331 is about 813.2226017518. Note that the first 3 decimals coincide. The cubic root of 661331 is about 87.1243652294.

Adding to 661331 its reverse (133166), we get a palindrome (794497).

It can be divided in two parts, 661 and 331, that multiplied together give a triangular number (218791 = T₆₆₁).

The spelling of 661331 in words is "six hundred sixty-one thousand, three hundred thirty-one".