21015221525 has 6 divisors (see below), whose sum is σ = 26058874722. Its totient is φ = 16812177200.

The previous prime is 21015221503. The next prime is 21015221533. The reversal of 21015221525 is 52512251012.

It is a happy number.

It can be written as a sum of positive squares in 3 ways, for example, as 4435826404 + 16579395121 = 66602^2 + 128761^2 .

It is not a de Polignac number, because 21015221525 - 2¹² = 21015217429 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21015221494 and 21015221503.

It is a congruent number.

It is an unprimeable number.

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 5 ways as a sum of consecutive naturals, for example, 420304406 + ... + 420304455.

It is an arithmetic number, because the mean of its divisors is an integer number (4343145787).

Almost surely, 2^21015221525 is an apocalyptic number.

21015221525 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21015221525 is a deficient number, since it is larger than the sum of its proper divisors (5043653197).

21015221525 is an equidigital number, since it uses as much as digits as its factorization.

21015221525 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 840608871 (or 840608866 counting only the distinct ones).

The product of its (nonzero) digits is 2000, while the sum is 26.

Adding to 21015221525 its reverse (52512251012), we get a palindrome (73527472537).

The spelling of 21015221525 in words is "twenty-one billion, fifteen million, two hundred twenty-one thousand, five hundred twenty-five".