1265689991 has 4 divisors (see below), whose sum is σ = 1280939352. Its totient is φ = 1250440632.

The previous prime is 1265689951. The next prime is 1265690009. The reversal of 1265689991 is 1999865621.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1999865621 = 13 ⋅153835817.

It is a cyclic number.

It is not a de Polignac number, because 1265689991 - 2⁶ = 1265689927 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 (1265689951) 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, 7624556 + ... + 7624721.

It is an arithmetic number, because the mean of its divisors is an integer number (320234838).

Almost surely, 2^1265689991 is an apocalyptic number.

1265689991 is a deficient number, since it is larger than the sum of its proper divisors (15249361).

1265689991 is an equidigital number, since it uses as much as digits as its factorization.

1265689991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15249360.

The product of its digits is 2099520, while the sum is 56.

The square root of 1265689991 is about 35576.5370855568. The cubic root of 1265689991 is about 1081.7056926219.

The spelling of 1265689991 in words is "one billion, two hundred sixty-five million, six hundred eighty-nine thousand, nine hundred ninety-one".