661881 has 16 divisors (see below), whose sum is σ = 995328. Its totient is φ = 387600.

The previous prime is 661879. The next prime is 661883. The reversal of 661881 is 188166.

661881 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is an interprime number because it is at equal distance from previous prime (661879) and next prime (661883).

It is not a de Polignac number, because 661881 - 2¹ = 661879 is a prime.

It is a super-2 number, since 2×661881² = 876172916322, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (661883) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 700 + ... + 1346.

It is an arithmetic number, because the mean of its divisors is an integer number (62208).

2⁶⁶¹⁸⁸¹ is an apocalyptic number.

It is an amenable number.

661881 is a deficient number, since it is larger than the sum of its proper divisors (333447).

661881 is a wasteful number, since it uses less digits than its factorization.

661881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 692.

The product of its digits is 2304, while the sum is 30.

The square root of 661881 is about 813.5606922658. The cubic root of 661881 is about 87.1485110420.

The spelling of 661881 in words is "six hundred sixty-one thousand, eight hundred eighty-one".