1808981861 has 2 divisors, whose sum is σ = 1808981862. Its totient is φ = 1808981860.

The previous prime is 1808981851. The next prime is 1808981873. The reversal of 1808981861 is 1681898081.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1797251236 + 11730625 = 42394^2 + 3425^2 .

It is an emirp because it is prime and its reverse (1681898081) is a distict prime. It is also a bemirp because it and its reverse can be mirrored producing other two distinct primes, 1981868081 and 1808681891.

It is a cyclic number.

It is not a de Polignac number, because 1808981861 - 2¹⁰ = 1808980837 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1808981851) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 904490930 + 904490931.

It is an arithmetic number, because the mean of its divisors is an integer number (904490931).

Almost surely, 2^1808981861 is an apocalyptic number.

It is an amenable number.

1808981861 is a deficient number, since it is larger than the sum of its proper divisors (1).

1808981861 is an equidigital number, since it uses as much as digits as its factorization.

1808981861 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 221184, while the sum is 50.

The square root of 1808981861 is about 42532.1273980035. The cubic root of 1808981861 is about 1218.4603575706.

The spelling of 1808981861 in words is "one billion, eight hundred eight million, nine hundred eighty-one thousand, eight hundred sixty-one".