1261305205 has 4 divisors (see below), whose sum is σ = 1513566252. Its totient is φ = 1009044160.

The previous prime is 1261305203. The next prime is 1261305239. The reversal of 1261305205 is 5025031621.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 5025031621 = 383 ⋅13120187.

It can be written as a sum of positive squares in 2 ways, for example, as 462508036 + 798797169 = 21506^2 + 28263^2 .

It is not a de Polignac number, because 1261305205 - 2¹ = 1261305203 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 1261305205.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1261305203) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 126130516 + ... + 126130525.

It is an arithmetic number, because the mean of its divisors is an integer number (378391563).

Almost surely, 2^1261305205 is an apocalyptic number.

It is an amenable number.

1261305205 is a deficient number, since it is larger than the sum of its proper divisors (252261047).

1261305205 is an equidigital number, since it uses as much as digits as its factorization.

1261305205 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 252261046.

The product of its (nonzero) digits is 1800, while the sum is 25.

The square root of 1261305205 is about 35514.8589325651. The cubic root of 1261305205 is about 1080.4551136858.

Adding to 1261305205 its reverse (5025031621), we get a palindrome (6286336826).

The spelling of 1261305205 in words is "one billion, two hundred sixty-one million, three hundred five thousand, two hundred five".