21515420125 has 8 divisors (see below), whose sum is σ = 26851244472. Its totient is φ = 17212336000.

The previous prime is 21515420057. The next prime is 21515420149. The reversal of 21515420125 is 52102451512.

It can be written as a sum of positive squares in 4 ways, for example, as 46430596 + 21468989529 = 6814^2 + 146523^2 .

It is not a de Polignac number, because 21515420125 - 2¹⁷ = 21515289053 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21515420093 and 21515420102.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 86061556 + ... + 86061805.

It is an arithmetic number, because the mean of its divisors is an integer number (3356405559).

Almost surely, 2^21515420125 is an apocalyptic number.

21515420125 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21515420125 is a deficient number, since it is larger than the sum of its proper divisors (5335824347).

21515420125 is an equidigital number, since it uses as much as digits as its factorization.

21515420125 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 172123376 (or 172123366 counting only the distinct ones).

The product of its (nonzero) digits is 4000, while the sum is 28.

Adding to 21515420125 its reverse (52102451512), we get a palindrome (73617871637).

The spelling of 21515420125 in words is "twenty-one billion, five hundred fifteen million, four hundred twenty thousand, one hundred twenty-five".