661221 has 12 divisors (see below), whose sum is σ = 1042080. Its totient is φ = 400680.

The previous prime is 661217. The next prime is 661231. The reversal of 661221 is 122166.

It is a happy number.

661221 is a `hidden beast` number, since 661 + 2 + 2 + 1 = 666.

661221 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 661221 - 2² = 661217 is a prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 661194 and 661203.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661201) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 3241 + ... + 3438.

It is an arithmetic number, because the mean of its divisors is an integer number (86840).

2⁶⁶¹²²¹ is an apocalyptic number.

It is an amenable number.

661221 is a deficient number, since it is larger than the sum of its proper divisors (380859).

661221 is a wasteful number, since it uses less digits than its factorization.

661221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6696 (or 6693 counting only the distinct ones).

The product of its digits is 144, while the sum is 18.

The square root of 661221 is about 813.1549667806. The cubic root of 661221 is about 87.1195344606.

Adding to 661221 its reverse (122166), we get a palindrome (783387).

The spelling of 661221 in words is "six hundred sixty-one thousand, two hundred twenty-one".