20999987 has 4 divisors (see below), whose sum is σ = 21091920. Its totient is φ = 20908056.

The previous prime is 20999977. The next prime is 20999999. The reversal of 20999987 is 78999902.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 78999902 = 2 ⋅39499951.

It is a cyclic number.

It is not a de Polignac number, because 20999987 - 2¹⁰ = 20998963 is a prime.

It is a fibodiv number, since the Fibonacci-like sequence with seeds 20 and 999987 contains 20999987 itself.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20999917) 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, 45623 + ... + 46080.

It is an arithmetic number, because the mean of its divisors is an integer number (5272980).

Almost surely, 2^20999987 is an apocalyptic number.

20999987 is a deficient number, since it is larger than the sum of its proper divisors (91933).

20999987 is an equidigital number, since it uses as much as digits as its factorization.

20999987 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 91932.

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

The square root of 20999987 is about 4582.5742765393. The cubic root of 20999987 is about 275.8923607079.

The spelling of 20999987 in words is "twenty million, nine hundred ninety-nine thousand, nine hundred eighty-seven".