221661 has 12 divisors (see below), whose sum is σ = 349440. Its totient is φ = 134280.
The previous prime is 221659. The next prime is 221671. The reversal of 221661 is 166122.
It is a happy number.
221661 is a `hidden beast` number, since 2 + 2 + 1 + 661 = 666.
It is not a de Polignac number, because 221661 - 21 = 221659 is a prime.
It is a plaindrome in base 14.
It is a congruent number.
It is not an unprimeable number, because it can be changed into a prime (221621) by changing a digit.
It is a pernicious number, because its binary representation contains a prime number (11) of ones.
It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1021 + ... + 1218.
It is an arithmetic number, because the mean of its divisors is an integer number (29120).
2221661 is an apocalyptic number.
It is an amenable number.
221661 is a deficient number, since it is larger than the sum of its proper divisors (127779).
221661 is a wasteful number, since it uses less digits than its factorization.
221661 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 2256 (or 2253 counting only the distinct ones).
The product of its digits is 144, while the sum is 18.
The square root of 221661 is about 470.8088784210. The cubic root of 221661 is about 60.5196530191.
Adding to 221661 its reverse (166122), we get a palindrome (387783).
The spelling of 221661 in words is "two hundred twenty-one thousand, six hundred sixty-one".
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