2109121821 has 20 divisors (see below), whose sum is σ = 3159733500. Its totient is φ = 1402033536.

The previous prime is 2109121799. The next prime is 2109121843. The reversal of 2109121821 is 1281219012.

It is an interprime number because it is at equal distance from previous prime (2109121799) and next prime (2109121843).

It can be written as a sum of positive squares in 2 ways, for example, as 1843757721 + 265364100 = 42939^2 + 16290^2 .

It is not a de Polignac number, because 2109121821 - 2¹⁴ = 2109105437 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2109121891) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 9036 + ... + 65573.

It is an arithmetic number, because the mean of its divisors is an integer number (157986675).

Almost surely, 2^2109121821 is an apocalyptic number.

It is an amenable number.

2109121821 is a deficient number, since it is larger than the sum of its proper divisors (1050611679).

2109121821 is an equidigital number, since it uses as much as digits as its factorization.

2109121821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 74970 (or 74961 counting only the distinct ones).

The product of its (nonzero) digits is 576, while the sum is 27.

The square root of 2109121821 is about 45925.1763306359. The cubic root of 2109121821 is about 1282.4306477323.

The spelling of 2109121821 in words is "two billion, one hundred nine million, one hundred twenty-one thousand, eight hundred twenty-one".