21011001990 has 128 divisors (see below), whose sum is σ = 59903193600. Its totient is φ = 4659056640.

The previous prime is 21011001989. The next prime is 21011002031. The reversal of 21011001990 is 9910011012.

It is a self number, because there is not a number n which added to its sum of digits gives 21011001990.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 124054 + ... + 239606.

It is an arithmetic number, because the mean of its divisors is an integer number (467993700).

Almost surely, 2^21011001990 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21011001990, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29951596800).

21011001990 is an abundant number, since it is smaller than the sum of its proper divisors (38892191610).

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

21011001990 is a wasteful number, since it uses less digits than its factorization.

21011001990 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 115622.

The product of its (nonzero) digits is 162, while the sum is 24.

The spelling of 21011001990 in words is "twenty-one billion, eleven million, one thousand, nine hundred ninety".