1261565521 has 4 divisors (see below), whose sum is σ = 1262939200. Its totient is φ = 1260191844.

The previous prime is 1261565507. The next prime is 1261565581. The reversal of 1261565521 is 1255651621.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 1261565521 - 2⁹ = 1261565009 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1261565581) 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, 685461 + ... + 687298.

It is an arithmetic number, because the mean of its divisors is an integer number (315734800).

Almost surely, 2^1261565521 is an apocalyptic number.

It is an amenable number.

1261565521 is a deficient number, since it is larger than the sum of its proper divisors (1373679).

1261565521 is an equidigital number, since it uses as much as digits as its factorization.

1261565521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1373678.

The product of its digits is 18000, while the sum is 34.

The square root of 1261565521 is about 35518.5236320430. The cubic root of 1261565521 is about 1080.5294389179.

The spelling of 1261565521 in words is "one billion, two hundred sixty-one million, five hundred sixty-five thousand, five hundred twenty-one".