61661 has 4 divisors (see below), whose sum is σ = 62172. Its totient is φ = 61152.

The previous prime is 61657. The next prime is 61667. The reversal of 61661 is 16616.

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 can be written as a sum of positive squares in 2 ways, for example, as 28900 + 32761 = 170^2 + 181^2 .

It is a cyclic number.

It is not a de Polignac number, because 61661 - 2² = 61657 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (61667) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 41 + ... + 353.

It is an arithmetic number, because the mean of its divisors is an integer number (15543).

2⁶¹⁶⁶¹ is an apocalyptic number.

It is an amenable number.

61661 is a deficient number, since it is larger than the sum of its proper divisors (511).

61661 is a wasteful number, since it uses less digits than its factorization.

61661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 510.

The product of its digits is 216, while the sum is 20.

The square root of 61661 is about 248.3163305141. The cubic root of 61661 is about 39.5066484563.

The spelling of 61661 in words is "sixty-one thousand, six hundred sixty-one".