1291891691 has 4 divisors (see below), whose sum is σ = 1292687352. Its totient is φ = 1291096032.

The previous prime is 1291891651. The next prime is 1291891703. The reversal of 1291891691 is 1961981921.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1961981921 = 29 ⋅67654549.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1291891691 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1291891621) 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, 395390 + ... + 398643.

It is an arithmetic number, because the mean of its divisors is an integer number (323171838).

Almost surely, 2^1291891691 is an apocalyptic number.

1291891691 is a deficient number, since it is larger than the sum of its proper divisors (795661).

1291891691 is an equidigital number, since it uses as much as digits as its factorization.

1291891691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 795660.

The product of its digits is 69984, while the sum is 47.

The square root of 1291891691 is about 35942.8948611544. The cubic root of 1291891691 is about 1089.1190848486.

The spelling of 1291891691 in words is "one billion, two hundred ninety-one million, eight hundred ninety-one thousand, six hundred ninety-one".