3815721891 has 32 divisors (see below), whose sum is σ = 5745358080. Its totient is φ = 2502327168.

The previous prime is 3815721887. The next prime is 3815721901. The reversal of 3815721891 is 1981275183.

3815721891 is a `hidden beast` number, since 381 + 57 + 218 + 9 + 1 = 666.

It is not a de Polignac number, because 3815721891 - 2² = 3815721887 is a prime.

It is not an unprimeable number, because it can be changed into a prime (3815721881) 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 31 ways as a sum of consecutive naturals, for example, 2146395 + ... + 2148171.

It is an arithmetic number, because the mean of its divisors is an integer number (179542440).

Almost surely, 2^3815721891 is an apocalyptic number.

3815721891 is a deficient number, since it is larger than the sum of its proper divisors (1929636189).

3815721891 is a wasteful number, since it uses less digits than its factorization.

3815721891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3040 (or 3034 counting only the distinct ones).

The product of its digits is 120960, while the sum is 45.

The square root of 3815721891 is about 61771.5297770745. The cubic root of 3815721891 is about 1562.6398829945.

The spelling of 3815721891 in words is "three billion, eight hundred fifteen million, seven hundred twenty-one thousand, eight hundred ninety-one".