20987999 has 6 divisors (see below), whose sum is σ = 21489336. Its totient is φ = 20498100.

The previous prime is 20987971. The next prime is 20988007. The reversal of 20987999 is 99978902.

It is not a de Polignac number, because 20987999 - 2¹⁶ = 20922463 is a prime.

It is a super-2 number, since 2×20987999² = 880992204048002, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 20987999.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20987969) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 3827 + ... + 7524.

It is an arithmetic number, because the mean of its divisors is an integer number (3581556).

Almost surely, 2^20987999 is an apocalyptic number.

20987999 is a deficient number, since it is larger than the sum of its proper divisors (501337).

20987999 is an equidigital number, since it uses as much as digits as its factorization.

20987999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11437 (or 11394 counting only the distinct ones).

The product of its (nonzero) digits is 734832, while the sum is 53.

The square root of 20987999 is about 4581.2660913769. The cubic root of 20987999 is about 275.8398523076.

The spelling of 20987999 in words is "twenty million, nine hundred eighty-seven thousand, nine hundred ninety-nine".