21036311521 has 9 divisors (see below), whose sum is σ = 21543292179. Its totient is φ = 20541003336.

The previous prime is 21036311509. The next prime is 21036311591. The reversal of 21036311521 is 12511363012.

It is a happy number.

The square root of 21036311521 is 145039.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 20812390225 + 223921296 = 144265^2 + 14964^2 .

It is not a de Polignac number, because 21036311521 - 2⁵ = 21036311489 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21036311501) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 6234991 + ... + 6238363.

It is an arithmetic number, because the mean of its divisors is an integer number (2393699131).

Almost surely, 2^21036311521 is an apocalyptic number.

21036311521 is the 145039-th square number.

21036311521 is the 72520-th centered octagonal number.

It is an amenable number.

21036311521 is a deficient number, since it is larger than the sum of its proper divisors (506980658).

21036311521 is an frugal number, since it uses more digits than its factorization.

21036311521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6832 (or 3416 counting only the distinct ones).

The product of its (nonzero) digits is 1080, while the sum is 25.

Multiplying 21036311521 by its sum of digits (25), we get a square (525907788025 = 725195²).

Adding to 21036311521 its reverse (12511363012), we get a palindrome (33547674533).

The spelling of 21036311521 in words is "twenty-one billion, thirty-six million, three hundred eleven thousand, five hundred twenty-one".