1021809891 has 16 divisors (see below), whose sum is σ = 1422570240. Its totient is φ = 651166560.

The previous prime is 1021809889. The next prime is 1021809907. The reversal of 1021809891 is 1989081201.

It is not a de Polignac number, because 1021809891 - 2¹ = 1021809889 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1021809881) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 129405 + ... + 137073.

It is an arithmetic number, because the mean of its divisors is an integer number (88910640).

Almost surely, 2^1021809891 is an apocalyptic number.

1021809891 is a deficient number, since it is larger than the sum of its proper divisors (400760349).

1021809891 is a wasteful number, since it uses less digits than its factorization.

1021809891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9626.

The product of its (nonzero) digits is 10368, while the sum is 39.

The square root of 1021809891 is about 31965.7612297909. The cubic root of 1021809891 is about 1007.2177425215.

The spelling of 1021809891 in words is "one billion, twenty-one million, eight hundred nine thousand, eight hundred ninety-one".