2001211981 has 2 divisors, whose sum is σ = 2001211982. Its totient is φ = 2001211980.

The previous prime is 2001211943. The next prime is 2001212021. The reversal of 2001211981 is 1891121002.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 2001130756 + 81225 = 44734^2 + 285^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-2001211981 is a prime.

It is a super-2 number, since 2×2001211981² = 8009698785795888722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (2001211181) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1000605990 + 1000605991.

It is an arithmetic number, because the mean of its divisors is an integer number (1000605991).

Almost surely, 2^2001211981 is an apocalyptic number.

It is an amenable number.

2001211981 is a deficient number, since it is larger than the sum of its proper divisors (1).

2001211981 is an equidigital number, since it uses as much as digits as its factorization.

2001211981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 288, while the sum is 25.

The square root of 2001211981 is about 44734.9078572875. The cubic root of 2001211981 is about 1260.1754985663.

Adding to 2001211981 its reverse (1891121002), we get a palindrome (3892332983).

The spelling of 2001211981 in words is "two billion, one million, two hundred eleven thousand, nine hundred eighty-one".