221521251 has 16 divisors (see below), whose sum is σ = 345407744. Its totient is φ = 123639264.

The previous prime is 221521249. The next prime is 221521259. The reversal of 221521251 is 152125122.

It is not a de Polignac number, because 221521251 - 2¹ = 221521249 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (221521259) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 121756 + ... + 123561.

It is an arithmetic number, because the mean of its divisors is an integer number (21587984).

Almost surely, 2^221521251 is an apocalyptic number.

221521251 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

221521251 is a deficient number, since it is larger than the sum of its proper divisors (123886493).

221521251 is a wasteful number, since it uses less digits than its factorization.

221521251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 245370.

The product of its digits is 400, while the sum is 21.

The square root of 221521251 is about 14883.5899903216. The cubic root of 221521251 is about 605.0693188338.

Adding to 221521251 its reverse (152125122), we get a palindrome (373646373).

The spelling of 221521251 in words is "two hundred twenty-one million, five hundred twenty-one thousand, two hundred fifty-one".