21506993856 has 112 divisors (see below), whose sum is σ = 63264470880. Its totient is φ = 7164702720.

The previous prime is 21506993843. The next prime is 21506993923. The reversal of 21506993856 is 65839960512.

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 an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4353820 + ... + 4358756.

Almost surely, 2^21506993856 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 21506993856, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31632235440).

21506993856 is an abundant number, since it is smaller than the sum of its proper divisors (41757477024).

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

21506993856 is a wasteful number, since it uses less digits than its factorization.

21506993856 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7479 (or 7463 counting only the distinct ones).

The product of its (nonzero) digits is 3499200, while the sum is 54.

The spelling of 21506993856 in words is "twenty-one billion, five hundred six million, nine hundred ninety-three thousand, eight hundred fifty-six".