661321 has 2 divisors, whose sum is σ = 661322. Its totient is φ = 661320.

The previous prime is 661267. The next prime is 661327. The reversal of 661321 is 123166.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 657721 + 3600 = 811^2 + 60^2 .

It is a cyclic number.

It is not a de Polignac number, because 661321 - 2⁹ = 660809 is a prime.

It is not a weakly prime, because it can be changed into another prime (661327) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330660 + 330661.

It is an arithmetic number, because the mean of its divisors is an integer number (330661).

2⁶⁶¹³²¹ is an apocalyptic number.

It is an amenable number.

661321 is a deficient number, since it is larger than the sum of its proper divisors (1).

661321 is an equidigital number, since it uses as much as digits as its factorization.

661321 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 216, while the sum is 19.

The square root of 661321 is about 813.2164533505. The cubic root of 661321 is about 87.1239260908.

Adding to 661321 its reverse (123166), we get a palindrome (784487).

The spelling of 661321 in words is "six hundred sixty-one thousand, three hundred twenty-one".