1261243565 has 4 divisors (see below), whose sum is σ = 1513492284. Its totient is φ = 1008994848.

The previous prime is 1261243559. The next prime is 1261243601. The reversal of 1261243565 is 5653421621.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 971631241 + 289612324 = 31171^2 + 17018^2 .

It is a cyclic number.

It is not a de Polignac number, because 1261243565 - 2¹⁴ = 1261227181 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 126124352 + ... + 126124361.

It is an arithmetic number, because the mean of its divisors is an integer number (378373071).

Almost surely, 2^1261243565 is an apocalyptic number.

It is an amenable number.

1261243565 is a deficient number, since it is larger than the sum of its proper divisors (252248719).

1261243565 is an equidigital number, since it uses as much as digits as its factorization.

1261243565 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 252248718.

The product of its digits is 43200, while the sum is 35.

The square root of 1261243565 is about 35513.9911161784. The cubic root of 1261243565 is about 1080.4375127811.

The spelling of 1261243565 in words is "one billion, two hundred sixty-one million, two hundred forty-three thousand, five hundred sixty-five".