20987009 has 4 divisors (see below), whose sum is σ = 21077316. Its totient is φ = 20896704.

The previous prime is 20986991. The next prime is 20987023. The reversal of 20987009 is 90078902.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 3888784 + 17098225 = 1972^2 + 4135^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20987009 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 20987009.

It is not an unprimeable number, because it can be changed into a prime (20987059) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 44804 + ... + 45269.

It is an arithmetic number, because the mean of its divisors is an integer number (5269329).

Almost surely, 2^20987009 is an apocalyptic number.

It is an amenable number.

20987009 is a deficient number, since it is larger than the sum of its proper divisors (90307).

20987009 is an equidigital number, since it uses as much as digits as its factorization.

20987009 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 90306.

The product of its (nonzero) digits is 9072, while the sum is 35.

The square root of 20987009 is about 4581.1580413690. The cubic root of 20987009 is about 275.8355151346.

The spelling of 20987009 in words is "twenty million, nine hundred eighty-seven thousand, nine".