20809987 has 8 divisors (see below), whose sum is σ = 22756032. Its totient is φ = 18873000.

The previous prime is 20809961. The next prime is 20809991. The reversal of 20809987 is 78990802.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20809987 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20809387) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3112 + ... + 7162.

It is an arithmetic number, because the mean of its divisors is an integer number (2844504).

Almost surely, 2^20809987 is an apocalyptic number.

20809987 is a deficient number, since it is larger than the sum of its proper divisors (1946045).

20809987 is a wasteful number, since it uses less digits than its factorization.

20809987 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4529.

The product of its (nonzero) digits is 72576, while the sum is 43.

The square root of 20809987 is about 4561.7964663058. The cubic root of 20809987 is about 275.0577817977.

The spelling of 20809987 in words is "twenty million, eight hundred nine thousand, nine hundred eighty-seven".