21001555422 has 64 divisors (see below), whose sum is σ = 48523598400. Its totient is φ = 6811262784.

The previous prime is 21001555409. The next prime is 21001555429. The reversal of 21001555422 is 22455510012.

21001555422 is a `hidden beast` number, since 2 + 100 + 1 + 5 + 554 + 2 + 2 = 666.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21001555429) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 96954 + ... + 226722.

It is an arithmetic number, because the mean of its divisors is an integer number (758181225).

Almost surely, 2^21001555422 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21001555422, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24261799200).

21001555422 is an abundant number, since it is smaller than the sum of its proper divisors (27522042978).

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

21001555422 is an equidigital number, since it uses as much as digits as its factorization.

21001555422 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 129829 (or 129811 counting only the distinct ones).

The product of its (nonzero) digits is 4000, while the sum is 27.

The spelling of 21001555422 in words is "twenty-one billion, one million, five hundred fifty-five thousand, four hundred twenty-two".