21005261000 has 64 divisors (see below), whose sum is σ = 49385756160. Its totient is φ = 8362200000.

The previous prime is 21005260961. The next prime is 21005261023. The reversal of 21005261000 is 16250012.

It is a self number, because there is not a number n which added to its sum of digits gives 21005261000.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 161225 + ... + 260775.

It is an arithmetic number, because the mean of its divisors is an integer number (771652440).

Almost surely, 2^21005261000 is an apocalyptic number.

21005261000 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21005261000, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24692878080).

21005261000 is an abundant number, since it is smaller than the sum of its proper divisors (28380495160).

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

21005261000 is a wasteful number, since it uses less digits than its factorization.

21005261000 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 99783 (or 99769 counting only the distinct ones).

The product of its (nonzero) digits is 120, while the sum is 17.

The spelling of 21005261000 in words is "twenty-one billion, five million, two hundred sixty-one thousand".