21039987 has 16 divisors (see below), whose sum is σ = 28643328. Its totient is φ = 13734720.

The previous prime is 21039971. The next prime is 21039989. The reversal of 21039987 is 78993012.

It is not a de Polignac number, because 21039987 - 2⁴ = 21039971 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21039989) 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 15 ways as a sum of consecutive naturals, for example, 41578 + ... + 42080.

It is an arithmetic number, because the mean of its divisors is an integer number (1790208).

Almost surely, 2^21039987 is an apocalyptic number.

21039987 is a deficient number, since it is larger than the sum of its proper divisors (7603341).

21039987 is a wasteful number, since it uses less digits than its factorization.

21039987 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 770.

The product of its (nonzero) digits is 27216, while the sum is 39.

The square root of 21039987 is about 4586.9365594043. The cubic root of 21039987 is about 276.0674194677.

It can be divided in two parts, 2103 and 9987, that added together give a triangular number (12090 = T₁₅₅).

The spelling of 21039987 in words is "twenty-one million, thirty-nine thousand, nine hundred eighty-seven".