1491136861 has 4 divisors (see below), whose sum is σ = 1578850812. Its totient is φ = 1403422912.

The previous prime is 1491136849. The next prime is 1491136919. The reversal of 1491136861 is 1686311941.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1686311941 = 337 ⋅5003893.

It can be written as a sum of positive squares in 2 ways, for example, as 1300972761 + 190164100 = 36069^2 + 13790^2 .

It is a cyclic number.

It is not a de Polignac number, because 1491136861 - 2⁷ = 1491136733 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 (1491136811) 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, 43856950 + ... + 43856983.

It is an arithmetic number, because the mean of its divisors is an integer number (394712703).

Almost surely, 2^1491136861 is an apocalyptic number.

It is an amenable number.

1491136861 is a deficient number, since it is larger than the sum of its proper divisors (87713951).

1491136861 is an equidigital number, since it uses as much as digits as its factorization.

1491136861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 87713950.

The product of its digits is 31104, while the sum is 40.

The square root of 1491136861 is about 38615.2413044383. The cubic root of 1491136861 is about 1142.4551736072.

The spelling of 1491136861 in words is "one billion, four hundred ninety-one million, one hundred thirty-six thousand, eight hundred sixty-one".