21099599550 has 192 divisors, whose sum is σ = 59720463360. Its totient is φ = 5475133440.

The previous prime is 21099599531. The next prime is 21099599593. The reversal of 21099599550 is 5599599012.

It is a happy number.

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

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 12244989 + ... + 12246711.

It is an arithmetic number, because the mean of its divisors is an integer number (311044080).

Almost surely, 2^21099599550 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21099599550, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29860231680).

21099599550 is an abundant number, since it is smaller than the sum of its proper divisors (38620863810).

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

21099599550 is a wasteful number, since it uses less digits than its factorization.

21099599550 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1984 (or 1973 counting only the distinct ones).

The product of its (nonzero) digits is 1640250, while the sum is 54.

The spelling of 21099599550 in words is "twenty-one billion, ninety-nine million, five hundred ninety-nine thousand, five hundred fifty".