21139867728 has 240 divisors, whose sum is σ = 70837757760. Its totient is φ = 6018437376.

The previous prime is 21139867687. The next prime is 21139867747. The reversal of 21139867728 is 82776893112.

It is a happy number.

It is a Smith number, since the sum of its digits (54) coincides with the sum of the digits of its prime factors.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 6496950 + ... + 6500202.

It is an arithmetic number, because the mean of its divisors is an integer number (295157324).

Almost surely, 2^21139867728 is an apocalyptic number.

21139867728 is a gapful number since it is divisible by the number (28) 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 21139867728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35418878880).

21139867728 is an abundant number, since it is smaller than the sum of its proper divisors (49697890032).

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

21139867728 is a wasteful number, since it uses less digits than its factorization.

21139867728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3591 (or 3572 counting only the distinct ones).

The product of its digits is 2032128, while the sum is 54.

The spelling of 21139867728 in words is "twenty-one billion, one hundred thirty-nine million, eight hundred sixty-seven thousand, seven hundred twenty-eight".