21288138521 has 4 divisors (see below), whose sum is σ = 22925687652. Its totient is φ = 19650589392.

The previous prime is 21288138511. The next prime is 21288138533. The reversal of 21288138521 is 12583188212.

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

It can be written as a sum of positive squares in 2 ways, for example, as 9319778521 + 11968360000 = 96539^2 + 109400^2 .

It is a cyclic number.

It is not a de Polignac number, because 21288138521 - 2²⁶ = 21221029657 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21288138511) 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, 818774546 + ... + 818774571.

It is an arithmetic number, because the mean of its divisors is an integer number (5731421913).

Almost surely, 2^21288138521 is an apocalyptic number.

It is an amenable number.

21288138521 is a deficient number, since it is larger than the sum of its proper divisors (1637549131).

21288138521 is a wasteful number, since it uses less digits than its factorization.

21288138521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1637549130.

The product of its digits is 61440, while the sum is 41.

The spelling of 21288138521 in words is "twenty-one billion, two hundred eighty-eight million, one hundred thirty-eight thousand, five hundred twenty-one".