21645431225 has 12 divisors (see below), whose sum is σ = 29280365520. Its totient is φ = 15742131600.

The previous prime is 21645431221. The next prime is 21645431267. The reversal of 21645431225 is 52213454612.

It is not a de Polignac number, because 21645431225 - 2² = 21645431221 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21645431221) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 39355055 + ... + 39355604.

It is an arithmetic number, because the mean of its divisors is an integer number (2440030460).

Almost surely, 2^21645431225 is an apocalyptic number.

21645431225 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21645431225 is a deficient number, since it is larger than the sum of its proper divisors (7634934295).

21645431225 is a wasteful number, since it uses less digits than its factorization.

21645431225 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 78710680 (or 78710675 counting only the distinct ones).

The product of its digits is 57600, while the sum is 35.

Adding to 21645431225 its reverse (52213454612), we get a palindrome (73858885837).

The spelling of 21645431225 in words is "twenty-one billion, six hundred forty-five million, four hundred thirty-one thousand, two hundred twenty-five".