661553 has 2 divisors, whose sum is σ = 661554. Its totient is φ = 661552.

The previous prime is 661547. The next prime is 661603. The reversal of 661553 is 355166.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 659344 + 2209 = 812^2 + 47^2 .

It is a cyclic number.

It is not a de Polignac number, because 661553 - 2¹⁰ = 660529 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (661513) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330776 + 330777.

It is an arithmetic number, because the mean of its divisors is an integer number (330777).

2⁶⁶¹⁵⁵³ is an apocalyptic number.

It is an amenable number.

661553 is a deficient number, since it is larger than the sum of its proper divisors (1).

661553 is an equidigital number, since it uses as much as digits as its factorization.

661553 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2700, while the sum is 26.

The square root of 661553 is about 813.3590842918. The cubic root of 661553 is about 87.1341129681.

The spelling of 661553 in words is "six hundred sixty-one thousand, five hundred fifty-three".