20717987 has 4 divisors (see below), whose sum is σ = 20980320. Its totient is φ = 20455656.

The previous prime is 20717969. The next prime is 20717989. The reversal of 20717987 is 78971702.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 78971702 = 2 ⋅39485851.

It is a cyclic number.

It is not a de Polignac number, because 20717987 - 2¹⁰ = 20716963 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20717989) 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 3 ways as a sum of consecutive naturals, for example, 131048 + ... + 131205.

It is an arithmetic number, because the mean of its divisors is an integer number (5245080).

Almost surely, 2^20717987 is an apocalyptic number.

20717987 is a deficient number, since it is larger than the sum of its proper divisors (262333).

20717987 is an equidigital number, since it uses as much as digits as its factorization.

20717987 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 262332.

The product of its (nonzero) digits is 49392, while the sum is 41.

The square root of 20717987 is about 4551.7015499701. The cubic root of 20717987 is about 274.6518437097.

The spelling of 20717987 in words is "twenty million, seven hundred seventeen thousand, nine hundred eighty-seven".