21285120640 has 128 divisors (see below), whose sum is σ = 61575033600. Its totient is φ = 6868451328.

The previous prime is 21285120613. The next prime is 21285120643. The reversal of 21285120640 is 4602158212.

It is a tau number, because it is divible by the number of its divisors (128).

It is not an unprimeable number, because it can be changed into a prime (21285120643) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 63580 + ... + 215899.

It is an arithmetic number, because the mean of its divisors is an integer number (481054950).

Almost surely, 2^21285120640 is an apocalyptic number.

21285120640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21285120640 is an abundant number, since it is smaller than the sum of its proper divisors (40289912960).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21285120640 is a wasteful number, since it uses less digits than its factorization.

21285120640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 279522 (or 279510 counting only the distinct ones).

The product of its (nonzero) digits is 7680, while the sum is 31.

Adding to 21285120640 its reverse (4602158212), we get a palindrome (25887278852).

The spelling of 21285120640 in words is "twenty-one billion, two hundred eighty-five million, one hundred twenty thousand, six hundred forty".