21251051440 has 80 divisors (see below), whose sum is σ = 49831096320. Its totient is φ = 8427974400.

The previous prime is 21251051431. The next prime is 21251051443. The reversal of 21251051440 is 4415015212.

It is a tau number, because it is divible by the number of its divisors (80).

It is not an unprimeable number, because it can be changed into a prime (21251051443) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7814401 + ... + 7817119.

It is an arithmetic number, because the mean of its divisors is an integer number (622888704).

Almost surely, 2^21251051440 is an apocalyptic number.

21251051440 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 21251051440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24915548160).

21251051440 is an abundant number, since it is smaller than the sum of its proper divisors (28580044880).

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

21251051440 is a wasteful number, since it uses less digits than its factorization.

21251051440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3530 (or 3524 counting only the distinct ones).

The product of its (nonzero) digits is 1600, while the sum is 25.

Adding to 21251051440 its reverse (4415015212), we get a palindrome (25666066652).

The spelling of 21251051440 in words is "twenty-one billion, two hundred fifty-one million, fifty-one thousand, four hundred forty".