1261991823 has 4 divisors (see below), whose sum is σ = 1682655768. Its totient is φ = 841327880.

The previous prime is 1261991789. The next prime is 1261991827. The reversal of 1261991823 is 3281991621.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 3281991621 = 3 ⋅1093997207.

It is a cyclic number.

It is not a de Polignac number, because 1261991823 - 2¹⁰ = 1261990799 is a prime.

It is a super-2 number, since 2×1261991823² = 3185246722637726658, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1261991827) 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, 210331968 + ... + 210331973.

It is an arithmetic number, because the mean of its divisors is an integer number (420663942).

Almost surely, 2^1261991823 is an apocalyptic number.

1261991823 is a deficient number, since it is larger than the sum of its proper divisors (420663945).

1261991823 is an equidigital number, since it uses as much as digits as its factorization.

1261991823 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 420663944.

The product of its digits is 46656, while the sum is 42.

The square root of 1261991823 is about 35524.5242473421. The cubic root of 1261991823 is about 1080.6511342713.

The spelling of 1261991823 in words is "one billion, two hundred sixty-one million, nine hundred ninety-one thousand, eight hundred twenty-three".