221788 has 18 divisors (see below), whose sum is σ = 448616. Its totient is φ = 93984.

The previous prime is 221773. The next prime is 221797. The reversal of 221788 is 887122.

221788 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a Harshad number since it is a multiple of its sum of digits (28).

It is a plaindrome in base 15.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 2448 + ... + 2536.

221788 is a Friedman number, since it can be written as 7*((81+8)*2)^2, using all its digits and the basic arithmetic operations.

2²²¹⁷⁸⁸ is an apocalyptic number.

221788 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

221788 is an abundant number, since it is smaller than the sum of its proper divisors (226828).

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

221788 is an equidigital number, since it uses as much as digits as its factorization.

221788 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 189 (or 98 counting only the distinct ones).

The product of its digits is 1792, while the sum is 28.

The square root of 221788 is about 470.9437333695. The cubic root of 221788 is about 60.5312089965.

Multiplying 221788 by its sum of digits (28), we get a square (6210064 = 2492²).

221788 divided by its sum of digits (28) gives a square (7921 = 89²).

Multiplying 221788 by its product of digits (1792), we get a square (397444096 = 19936²).

The spelling of 221788 in words is "two hundred twenty-one thousand, seven hundred eighty-eight".