665221 has 2 divisors, whose sum is σ = 665222. Its totient is φ = 665220.

The previous prime is 665213. The next prime is 665233. The reversal of 665221 is 122566.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 429025 + 236196 = 655^2 + 486^2 .

It is a cyclic number.

It is not a de Polignac number, because 665221 - 2³ = 665213 is a prime.

It is an Ulam number.

It is a nialpdrome in base 10.

It is a junction number, because it is equal to n+sod(n) for n = 665192 and 665201.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (665201) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332610 + 332611.

It is an arithmetic number, because the mean of its divisors is an integer number (332611).

2⁶⁶⁵²²¹ is an apocalyptic number.

It is an amenable number.

665221 is a deficient number, since it is larger than the sum of its proper divisors (1).

665221 is an equidigital number, since it uses as much as digits as its factorization.

665221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 720, while the sum is 22.

The square root of 665221 is about 815.6108140529. The cubic root of 665221 is about 87.2948554671.

Adding to 665221 its reverse (122566), we get a palindrome (787787).

The spelling of 665221 in words is "six hundred sixty-five thousand, two hundred twenty-one".