221761 has 4 divisors (see below), whose sum is σ = 223024. Its totient is φ = 220500.

The previous prime is 221747. The next prime is 221773. The reversal of 221761 is 167122.

221761 = T₃₈₃ + T₃₈₄ + T₃₈₅.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 167122 = 2 ⋅83561.

It is a 3-Lehmer number, since φ(221761) divides (221761-1)³.

It is a cyclic number.

It is not a de Polignac number, because 221761 - 2⁵ = 221729 is a prime.

It is a super-2 number, since 2×221761² = 98355882242, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (221261) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 315 + ... + 736.

It is an arithmetic number, because the mean of its divisors is an integer number (55756).

2²²¹⁷⁶¹ is an apocalyptic number.

221761 is the 385-th centered triangular number.

It is an amenable number.

221761 is a deficient number, since it is larger than the sum of its proper divisors (1263).

221761 is a wasteful number, since it uses less digits than its factorization.

221761 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1262.

The product of its digits is 168, while the sum is 19.

The square root of 221761 is about 470.9150666522. The cubic root of 221761 is about 60.5287525832.

Adding to 221761 its reverse (167122), we get a palindrome (388883).

It can be divided in two parts, 2217 and 61, that added together give a triangular number (2278 = T₆₇).

The spelling of 221761 in words is "two hundred twenty-one thousand, seven hundred sixty-one".