21216017128 has 8 divisors (see below), whose sum is σ = 39780032130. Its totient is φ = 10608008560.

The previous prime is 21216017117. The next prime is 21216017159. The reversal of 21216017128 is 82171061212.

It can be written as a sum of positive squares in only one way, i.e., 13386952804 + 7829064324 = 115702^2 + 88482^2 .

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

It is a self number, because there is not a number n which added to its sum of digits gives 21216017128.

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 as a sum of consecutive naturals, namely, 1326001063 + ... + 1326001078.

Almost surely, 2^21216017128 is an apocalyptic number.

It is an amenable number.

21216017128 is a deficient number, since it is larger than the sum of its proper divisors (18564015002).

21216017128 is a wasteful number, since it uses less digits than its factorization.

21216017128 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2652002147 (or 2652002143 counting only the distinct ones).

The product of its (nonzero) digits is 2688, while the sum is 31.

The spelling of 21216017128 in words is "twenty-one billion, two hundred sixteen million, seventeen thousand, one hundred twenty-eight".