1561321205 has 18 divisors (see below), whose sum is σ = 1924863234. Its totient is φ = 1215764800.

The previous prime is 1561321187. The next prime is 1561321207. The reversal of 1561321205 is 5021231651.

It can be written as a sum of positive squares in 3 ways, for example, as 89908324 + 1471412881 = 9482^2 + 38359^2 .

It is not a de Polignac number, because 1561321205 - 2¹⁰ = 1561320181 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1561321207) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 3622340 + ... + 3622770.

Almost surely, 2^1561321205 is an apocalyptic number.

It is an amenable number.

1561321205 is a deficient number, since it is larger than the sum of its proper divisors (363542029).

1561321205 is an frugal number, since it uses more digits than its factorization.

1561321205 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 949 (or 477 counting only the distinct ones).

The product of its (nonzero) digits is 1800, while the sum is 26.

The square root of 1561321205 is about 39513.5572303988. The cubic root of 1561321205 is about 1160.1053226307.

Adding to 1561321205 its reverse (5021231651), we get a palindrome (6582552856).

The spelling of 1561321205 in words is "one billion, five hundred sixty-one million, three hundred twenty-one thousand, two hundred five".