21001465656 has 24 divisors (see below), whose sum is σ = 56878969680. Its totient is φ = 7000488528.

The previous prime is 21001465649. The next prime is 21001465691. The reversal of 21001465656 is 65656410012.

It is a tau number, because it is divible by the number of its divisors (24).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a self number, because there is not a number n which added to its sum of digits gives 21001465656.

It is a congruent number.

It is an unprimeable number.

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 in 5 ways as a sum of consecutive naturals, for example, 145843440 + ... + 145843583.

It is an arithmetic number, because the mean of its divisors is an integer number (2369957070).

Almost surely, 2^21001465656 is an apocalyptic number.

It is an amenable number.

21001465656 is an abundant number, since it is smaller than the sum of its proper divisors (35877504024).

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

21001465656 is a wasteful number, since it uses less digits than its factorization.

21001465656 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 291687035 (or 291687028 counting only the distinct ones).

The product of its (nonzero) digits is 43200, while the sum is 36.

Adding to 21001465656 its reverse (65656410012), we get a palindrome (86657875668).

The spelling of 21001465656 in words is "twenty-one billion, one million, four hundred sixty-five thousand, six hundred fifty-six".