2100021991 has 2 divisors, whose sum is σ = 2100021992. Its totient is φ = 2100021990.

The previous prime is 2100021961. The next prime is 2100022007. The reversal of 2100021991 is 1991200012.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 2100021991 - 2²¹ = 2097924839 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (2100021901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1050010995 + 1050010996.

It is an arithmetic number, because the mean of its divisors is an integer number (1050010996).

Almost surely, 2^2100021991 is an apocalyptic number.

2100021991 is a deficient number, since it is larger than the sum of its proper divisors (1).

2100021991 is an equidigital number, since it uses as much as digits as its factorization.

2100021991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 324, while the sum is 25.

The square root of 2100021991 is about 45825.9968904115. The cubic root of 2100021991 is about 1280.5836350062.

It can be divided in two parts, 2100021 and 991, that added together give a palindrome (2101012).

The spelling of 2100021991 in words is "two billion, one hundred million, twenty-one thousand, nine hundred ninety-one".