16531221 has 16 divisors (see below), whose sum is σ = 25777664. Its totient is φ = 9226224.

The previous prime is 16531219. The next prime is 16531223. The reversal of 16531221 is 12213561.

It is an interprime number because it is at equal distance from previous prime (16531219) and next prime (16531223).

It is not a de Polignac number, because 16531221 - 2¹ = 16531219 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 a congruent number.

It is not an unprimeable number, because it can be changed into a prime (16531223) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 8251 + ... + 10056.

It is an arithmetic number, because the mean of its divisors is an integer number (1611104).

Almost surely, 2^16531221 is an apocalyptic number.

It is an amenable number.

16531221 is a deficient number, since it is larger than the sum of its proper divisors (9246443).

16531221 is a wasteful number, since it uses less digits than its factorization.

16531221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18360.

The product of its digits is 360, while the sum is 21.

The square root of 16531221 is about 4065.8604255434. The cubic root of 16531221 is about 254.7426392290.

Adding to 16531221 its reverse (12213561), we get a palindrome (28744782).

The spelling of 16531221 in words is "sixteen million, five hundred thirty-one thousand, two hundred twenty-one".