661631 has 4 divisors (see below), whose sum is σ = 663264. Its totient is φ = 660000.

The previous prime is 661621. The next prime is 661663. The reversal of 661631 is 136166.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 661631 - 2¹⁰ = 660607 is a prime.

It is a super-2 number, since 2×661631² = 875511160322, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 661597 and 661606.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661621) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 311 + ... + 1191.

It is an arithmetic number, because the mean of its divisors is an integer number (165816).

2⁶⁶¹⁶³¹ is an apocalyptic number.

661631 is a deficient number, since it is larger than the sum of its proper divisors (1633).

661631 is an equidigital number, since it uses as much as digits as its factorization.

661631 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1632.

The product of its digits is 648, while the sum is 23.

The square root of 661631 is about 813.4070321801. The cubic root of 661631 is about 87.1375373315.

Adding to 661631 its reverse (136166), we get a palindrome (797797).

The spelling of 661631 in words is "six hundred sixty-one thousand, six hundred thirty-one".