1861091891 has 2 divisors, whose sum is σ = 1861091892. Its totient is φ = 1861091890.

The previous prime is 1861091879. The next prime is 1861091917. The reversal of 1861091891 is 1981901681.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 1861091891 - 2¹⁴ = 1861075507 is a prime.

It is a Sophie Germain prime.

It is not a weakly prime, because it can be changed into another prime (1861091861) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 930545945 + 930545946.

It is an arithmetic number, because the mean of its divisors is an integer number (930545946).

Almost surely, 2^1861091891 is an apocalyptic number.

1861091891 is the 23060-th centered heptagonal number.

1861091891 is a deficient number, since it is larger than the sum of its proper divisors (1).

1861091891 is an equidigital number, since it uses as much as digits as its factorization.

1861091891 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 31104, while the sum is 44.

The square root of 1861091891 is about 43140.3742566056. The cubic root of 1861091891 is about 1230.0495476548.

The spelling of 1861091891 in words is "one billion, eight hundred sixty-one million, ninety-one thousand, eight hundred ninety-one".