1261565581 has 2 divisors, whose sum is σ = 1261565582. Its totient is φ = 1261565580.

The previous prime is 1261565507. The next prime is 1261565603. The reversal of 1261565581 is 1855651621.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1211736100 + 49829481 = 34810^2 + 7059^2 .

It is an emirp because it is prime and its reverse (1855651621) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1261565581 - 2²¹ = 1259468429 is a prime.

It is a super-2 number, since 2×1261565581² = 3183095430327735122, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1261565881) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 630782790 + 630782791.

It is an arithmetic number, because the mean of its divisors is an integer number (630782791).

Almost surely, 2^1261565581 is an apocalyptic number.

It is an amenable number.

1261565581 is a deficient number, since it is larger than the sum of its proper divisors (1).

1261565581 is an equidigital number, since it uses as much as digits as its factorization.

1261565581 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 72000, while the sum is 40.

The square root of 1261565581 is about 35518.5244766727. The cubic root of 1261565581 is about 1080.5294560479.

The spelling of 1261565581 in words is "one billion, two hundred sixty-one million, five hundred sixty-five thousand, five hundred eighty-one".