21120645356456 has 8 divisors (see below), whose sum is σ = 39601210043370. Its totient is φ = 10560322678224.

The previous prime is 21120645356453. The next prime is 21120645356497. The reversal of 21120645356456 is 65465354602112.

It can be written as a sum of positive squares in only one way, i.e., 18884812983556 + 2235832372900 = 4345666^2 + 1495270^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is not an unprimeable number, because it can be changed into a prime (21120645356453) 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 as a sum of consecutive naturals, namely, 1320040334771 + ... + 1320040334786.

Almost surely, 2^{21120645356456} is an apocalyptic number.

It is an amenable number.

21120645356456 is a deficient number, since it is larger than the sum of its proper divisors (18480564686914).

21120645356456 is a wasteful number, since it uses less digits than its factorization.

21120645356456 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2640080669563 (or 2640080669559 counting only the distinct ones).

The product of its (nonzero) digits is 5184000, while the sum is 50.

Adding to 21120645356456 its reverse (65465354602112), we get a palindrome (86585999958568).

The spelling of 21120645356456 in words is "twenty-one trillion, one hundred twenty billion, six hundred forty-five million, three hundred fifty-six thousand, four hundred fifty-six".