221640 has 32 divisors (see below), whose sum is σ = 665280. Its totient is φ = 59072.

The previous prime is 221623. The next prime is 221653. The reversal of 221640 is 46122.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a nialpdrome in base 12.

It is an unprimeable number.

221640 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 804 + ... + 1043.

It is an arithmetic number, because the mean of its divisors is an integer number (20790).

2²²¹⁶⁴⁰ is an apocalyptic number.

221640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

221640 is an abundant number, since it is smaller than the sum of its proper divisors (443640).

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

221640 is a wasteful number, since it uses less digits than its factorization.

221640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1861 (or 1857 counting only the distinct ones).

The product of its (nonzero) digits is 96, while the sum is 15.

The square root of 221640 is about 470.7865758494. The cubic root of 221640 is about 60.5177417630.

Adding to 221640 its reverse (46122), we get a palindrome (267762).

It can be divided in two parts, 221 and 640, that added together give a triangular number (861 = T₄₁).

The spelling of 221640 in words is "two hundred twenty-one thousand, six hundred forty".