1221805728 has 576 divisors, whose sum is σ = 4504550400. Its totient is φ = 319334400.

The previous prime is 1221805709. The next prime is 1221805751. The reversal of 1221805728 is 8275081221.

1221805728 is a `hidden beast` number, since 1 + 2 + 2 + 1 + 80 + 572 + 8 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 1221805692 and 1221805701.

It is an unprimeable number.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 39413073 + ... + 39413103.

It is an arithmetic number, because the mean of its divisors is an integer number (7820400).

Almost surely, 2^1221805728 is an apocalyptic number.

1221805728 is a gapful number since it is divisible by the number (18) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 1221805728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2252275200).

1221805728 is an abundant number, since it is smaller than the sum of its proper divisors (3282744672).

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

1221805728 is a wasteful number, since it uses less digits than its factorization.

1221805728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 114 (or 89 counting only the distinct ones).

The product of its (nonzero) digits is 17920, while the sum is 36.

The square root of 1221805728 is about 34954.3377565646. The cubic root of 1221805728 is about 1069.0566489722.

Adding to 1221805728 its reverse (8275081221), we get a palindrome (9496886949).

The spelling of 1221805728 in words is "one billion, two hundred twenty-one million, eight hundred five thousand, seven hundred twenty-eight".