21151665664 has 40 divisors (see below), whose sum is σ = 42857332848. Its totient is φ = 10426859520.

The previous prime is 21151665653. The next prime is 21151665721. The reversal of 21151665664 is 46656615112.

It is a self number, because there is not a number n which added to its sum of digits gives 21151665664.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 254577 + ... + 327280.

Almost surely, 2^21151665664 is an apocalyptic number.

It is an amenable number.

21151665664 is an abundant number, since it is smaller than the sum of its proper divisors (21705667184).

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

21151665664 is an frugal number, since it uses more digits than its factorization.

21151665664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 581946 (or 581930 counting only the distinct ones).

The product of its digits is 259200, while the sum is 43.

The spelling of 21151665664 in words is "twenty-one billion, one hundred fifty-one million, six hundred sixty-five thousand, six hundred sixty-four".