21000647056 has 15 divisors (see below), whose sum is σ = 40689876801. Its totient is φ = 10500033696.

The previous prime is 21000647033. The next prime is 21000647069. The reversal of 21000647056 is 65074600012.

It is a happy number.

The square root of 21000647056 is 144916.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 11175872656 + 9824774400 = 105716^2 + 99120^2 .

It is a Duffinian 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 2 ways as a sum of consecutive naturals, for example, 561550 + ... + 597778.

Almost surely, 2^21000647056 is an apocalyptic number.

21000647056 is the 144916-th square number.

It is an amenable number.

21000647056 is a deficient number, since it is larger than the sum of its proper divisors (19689229745).

21000647056 is an frugal number, since it uses more digits than its factorization.

21000647056 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 72466 (or 36231 counting only the distinct ones).

The product of its (nonzero) digits is 10080, while the sum is 31.

The spelling of 21000647056 in words is "twenty-one billion, six hundred forty-seven thousand, fifty-six".