20509881 has 36 divisors (see below), whose sum is σ = 32998896. Its totient is φ = 11296320.

The previous prime is 20509843. The next prime is 20509891. The reversal of 20509881 is 18890502.

It is a happy number.

It is not a de Polignac number, because 20509881 - 2⁹ = 20509369 is a prime.

It is a super-2 number, since 2×20509881² = 841310437268322, which contains 22 as substring.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (20509831) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 247066 + ... + 247148.

It is an arithmetic number, because the mean of its divisors is an integer number (916636).

Almost surely, 2^20509881 is an apocalyptic number.

20509881 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

20509881 is a deficient number, since it is larger than the sum of its proper divisors (12489015).

20509881 is an equidigital number, since it uses as much as digits as its factorization.

20509881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 182 (or 134 counting only the distinct ones).

The product of its (nonzero) digits is 5760, while the sum is 33.

The square root of 20509881 is about 4528.7836115231. The cubic root of 20509881 is about 273.7291487632.

The spelling of 20509881 in words is "twenty million, five hundred nine thousand, eight hundred eighty-one".