19811861 has 2 divisors, whose sum is σ = 19811862. Its totient is φ = 19811860.

The previous prime is 19811849. The next prime is 19811867. The reversal of 19811861 is 16811891.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18748900 + 1062961 = 4330^2 + 1031^2 .

It is an emirp because it is prime and its reverse (16811891) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 19811861 - 2¹⁰ = 19810837 is a prime.

19811861 is a strobogrammatic number because it is the same when read upside-down.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19811867) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9905930 + 9905931.

It is an arithmetic number, because the mean of its divisors is an integer number (9905931).

Almost surely, 2^19811861 is an apocalyptic number.

It is an amenable number.

19811861 is a deficient number, since it is larger than the sum of its proper divisors (1).

19811861 is an equidigital number, since it uses as much as digits as its factorization.

19811861 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3456, while the sum is 35.

The square root of 19811861 is about 4451.0516734812. The cubic root of 19811861 is about 270.5879323665.

The spelling of 19811861 in words is "nineteen million, eight hundred eleven thousand, eight hundred sixty-one".