21261772128 has 144 divisors (see below), whose sum is σ = 57522286080. Its totient is φ = 6876349440.

The previous prime is 21261772117. The next prime is 21261772139. The reversal of 21261772128 is 82127716212.

It is an interprime number because it is at equal distance from previous prime (21261772117) and next prime (21261772139).

It is a congruent 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 23 ways as a sum of consecutive naturals, for example, 57933801 + ... + 57934167.

It is an arithmetic number, because the mean of its divisors is an integer number (399460320).

Almost surely, 2^21261772128 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21261772128, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28761143040).

21261772128 is an abundant number, since it is smaller than the sum of its proper divisors (36260513952).

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

21261772128 is a wasteful number, since it uses less digits than its factorization.

21261772128 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 821 (or 772 counting only the distinct ones).

The product of its digits is 37632, while the sum is 39.

The spelling of 21261772128 in words is "twenty-one billion, two hundred sixty-one million, seven hundred seventy-two thousand, one hundred twenty-eight".