1261691891 has 8 divisors (see below), whose sum is σ = 1274661360. Its totient is φ = 1248744448.

The previous prime is 1261691863. The next prime is 1261691927. The reversal of 1261691891 is 1981961621.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1261691891 - 2¹⁴ = 1261675507 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1261691801) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 125375 + ... + 135063.

It is an arithmetic number, because the mean of its divisors is an integer number (159332670).

Almost surely, 2^1261691891 is an apocalyptic number.

1261691891 is a deficient number, since it is larger than the sum of its proper divisors (12969469).

1261691891 is a wasteful number, since it uses less digits than its factorization.

1261691891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11013.

The product of its digits is 46656, while the sum is 44.

The square root of 1261691891 is about 35520.3025184190. The cubic root of 1261691891 is about 1080.5655163006.

The spelling of 1261691891 in words is "one billion, two hundred sixty-one million, six hundred ninety-one thousand, eight hundred ninety-one".