181819091921 has 2 divisors, whose sum is σ = 181819091922. Its totient is φ = 181819091920.

The previous prime is 181819091873. The next prime is 181819091957. The reversal of 181819091921 is 129190918181.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 178729399696 + 3089692225 = 422764^2 + 55585^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-181819091921 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 181819091921.

It is not a weakly prime, because it can be changed into another prime (181819091021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 90909545960 + 90909545961.

It is an arithmetic number, because the mean of its divisors is an integer number (90909545961).

Almost surely, 2^181819091921 is an apocalyptic number.

It is an amenable number.

181819091921 is a deficient number, since it is larger than the sum of its proper divisors (1).

181819091921 is an equidigital number, since it uses as much as digits as its factorization.

181819091921 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 93312, while the sum is 50.

The spelling of 181819091921 in words is "one hundred eighty-one billion, eight hundred nineteen million, ninety-one thousand, nine hundred twenty-one".