2181988021 has 2 divisors, whose sum is σ = 2181988022. Its totient is φ = 2181988020.

The previous prime is 2181987959. The next prime is 2181988037. The reversal of 2181988021 is 1208891812.

2181988021 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1437243921 + 744744100 = 37911^2 + 27290^2 .

It is a cyclic number.

It is not a de Polignac number, because 2181988021 - 2¹⁷ = 2181856949 is a prime.

It is a super-2 number, since 2×2181988021² = 9522143447574992882, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (2181988121) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1090994010 + 1090994011.

It is an arithmetic number, because the mean of its divisors is an integer number (1090994011).

Almost surely, 2^2181988021 is an apocalyptic number.

It is an amenable number.

2181988021 is a deficient number, since it is larger than the sum of its proper divisors (1).

2181988021 is an equidigital number, since it uses as much as digits as its factorization.

2181988021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 18432, while the sum is 40.

The square root of 2181988021 is about 46711.7546341389. The cubic root of 2181988021 is about 1297.0322876931.

The spelling of 2181988021 in words is "two billion, one hundred eighty-one million, nine hundred eighty-eight thousand, twenty-one".