221638521 has 16 divisors (see below), whose sum is σ = 318799040. Its totient is φ = 136157760.

The previous prime is 221638513. The next prime is 221638531. The reversal of 221638521 is 125836122.

It is not a de Polignac number, because 221638521 - 2³ = 221638513 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (221638531) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 19551 + ... + 28731.

It is an arithmetic number, because the mean of its divisors is an integer number (19924940).

Almost surely, 2^221638521 is an apocalyptic number.

It is an amenable number.

221638521 is a deficient number, since it is larger than the sum of its proper divisors (97160519).

221638521 is a wasteful number, since it uses less digits than its factorization.

221638521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9816.

The product of its digits is 5760, while the sum is 30.

The square root of 221638521 is about 14887.5290427928. The cubic root of 221638521 is about 605.1760715137.

The spelling of 221638521 in words is "two hundred twenty-one million, six hundred thirty-eight thousand, five hundred twenty-one".