18401221566 has 288 divisors, whose sum is σ = 53711592480. Its totient is φ = 4496228352.

The previous prime is 18401221541. The next prime is 18401221567. The reversal of 18401221566 is 66512210481.

It is a happy number.

18401221566 is a `hidden beast` number, since 1 + 84 + 0 + 12 + 2 + 1 + 566 = 666.

It is a self number, because there is not a number n which added to its sum of digits gives 18401221566.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18401221567) by changing a digit.

It is a polite number, since it can be written in 143 ways as a sum of consecutive naturals, for example, 13059070 + ... + 13060478.

It is an arithmetic number, because the mean of its divisors is an integer number (186498585).

Almost surely, 2^18401221566 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 18401221566, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26855796240).

18401221566 is an abundant number, since it is smaller than the sum of its proper divisors (35310370914).

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

18401221566 is a wasteful number, since it uses less digits than its factorization.

18401221566 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1528 (or 1518 counting only the distinct ones).

The product of its (nonzero) digits is 23040, while the sum is 36.

The spelling of 18401221566 in words is "eighteen billion, four hundred one million, two hundred twenty-one thousand, five hundred sixty-six".