21251528987 has 4 divisors (see below), whose sum is σ = 22886262000. Its totient is φ = 19616795976.

The previous prime is 21251528927. The next prime is 21251528989. The reversal of 21251528987 is 78982515212.

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

It is a cyclic number.

It is not a de Polignac number, because 21251528987 - 2⁶ = 21251528923 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21251528989) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 817366487 + ... + 817366512.

It is an arithmetic number, because the mean of its divisors is an integer number (5721565500).

Almost surely, 2^21251528987 is an apocalyptic number.

21251528987 is a deficient number, since it is larger than the sum of its proper divisors (1634733013).

21251528987 is a wasteful number, since it uses less digits than its factorization.

21251528987 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1634733012.

The product of its digits is 806400, while the sum is 50.

The spelling of 21251528987 in words is "twenty-one billion, two hundred fifty-one million, five hundred twenty-eight thousand, nine hundred eighty-seven".