555561661 has 2 divisors, whose sum is σ = 555561662. Its totient is φ = 555561660.

The previous prime is 555561659. The next prime is 555561679. The reversal of 555561661 is 166165555.

555561661 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 483736036 + 71825625 = 21994^2 + 8475^2 .

It is a cyclic number.

It is not a de Polignac number, because 555561661 - 2¹ = 555561659 is a prime.

Together with 555561659, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (555561361) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 277780830 + 277780831.

It is an arithmetic number, because the mean of its divisors is an integer number (277780831).

Almost surely, 2^555561661 is an apocalyptic number.

It is an amenable number.

555561661 is a deficient number, since it is larger than the sum of its proper divisors (1).

555561661 is an equidigital number, since it uses as much as digits as its factorization.

555561661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 135000, while the sum is 40.

The square root of 555561661 is about 23570.3555552308. The cubic root of 555561661 is about 822.0737028966.

The spelling of 555561661 in words is "five hundred fifty-five million, five hundred sixty-one thousand, six hundred sixty-one".