2021191981 has 2 divisors, whose sum is σ = 2021191982. Its totient is φ = 2021191980.

The previous prime is 2021191903. The next prime is 2021192009. The reversal of 2021191981 is 1891911202.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1129632100 + 891559881 = 33610^2 + 29859^2 .

It is a cyclic number.

It is not a de Polignac number, because 2021191981 - 2¹⁵ = 2021159213 is a prime.

It is a super-2 number, since 2×2021191981² = 8170434048117408722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (2021141981) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1010595990 + 1010595991.

It is an arithmetic number, because the mean of its divisors is an integer number (1010595991).

Almost surely, 2^2021191981 is an apocalyptic number.

It is an amenable number.

2021191981 is a deficient number, since it is larger than the sum of its proper divisors (1).

2021191981 is an equidigital number, since it uses as much as digits as its factorization.

2021191981 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2592, while the sum is 34.

The square root of 2021191981 is about 44957.6687674083. The cubic root of 2021191981 is about 1264.3554614114.

The spelling of 2021191981 in words is "two billion, twenty-one million, one hundred ninety-one thousand, nine hundred eighty-one".