210661 has 6 divisors (see below), whose sum is σ = 231686. Its totient is φ = 191400.

The previous prime is 210659. The next prime is 210671. The reversal of 210661 is 166012.

It can be written as a sum of positive squares in only one way, i.e., 108900 + 101761 = 330^2 + 319^2 .

It is not a de Polignac number, because 210661 - 2¹ = 210659 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (210601) 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 5 ways as a sum of consecutive naturals, for example, 750 + ... + 991.

2²¹⁰⁶⁶¹ is an apocalyptic number.

It is an amenable number.

210661 is a deficient number, since it is larger than the sum of its proper divisors (21025).

210661 is a wasteful number, since it uses less digits than its factorization.

210661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1763 (or 1752 counting only the distinct ones).

The product of its (nonzero) digits is 72, while the sum is 16.

The square root of 210661 is about 458.9782129906. The cubic root of 210661 is about 59.5015182156.

Adding to 210661 its reverse (166012), we get a palindrome (376673).

The spelling of 210661 in words is "two hundred ten thousand, six hundred sixty-one".