20091021 has 16 divisors (see below), whose sum is σ = 27522048. Its totient is φ = 13032000.

The previous prime is 20090977. The next prime is 20091023. The reversal of 20091021 is 12019002.

It is a happy number.

It is not a de Polignac number, because 20091021 - 2⁷ = 20090893 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20091023) 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, 17940 + ... + 19026.

It is an arithmetic number, because the mean of its divisors is an integer number (1720128).

Almost surely, 2^20091021 is an apocalyptic number.

It is an amenable number.

20091021 is a deficient number, since it is larger than the sum of its proper divisors (7431027).

20091021 is a wasteful number, since it uses less digits than its factorization.

20091021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1252.

The product of its (nonzero) digits is 36, while the sum is 15.

The square root of 20091021 is about 4482.3008600494. The cubic root of 20091021 is about 271.8529202309.

The spelling of 20091021 in words is "twenty million, ninety-one thousand, twenty-one".