81351221 has 6 divisors (see below), whose sum is σ = 94633110. Its totient is φ = 69729576.

The previous prime is 81351209. The next prime is 81351241. The reversal of 81351221 is 12215318.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 48804196 + 32547025 = 6986^2 + 5705^2 .

It is not a de Polignac number, because 81351221 - 2¹⁰ = 81350197 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81351241) 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 5 ways as a sum of consecutive naturals, for example, 830066 + ... + 830163.

It is an arithmetic number, because the mean of its divisors is an integer number (15772185).

Almost surely, 2^81351221 is an apocalyptic number.

It is an amenable number.

81351221 is a deficient number, since it is larger than the sum of its proper divisors (13281889).

81351221 is a wasteful number, since it uses less digits than its factorization.

81351221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1660243 (or 1660236 counting only the distinct ones).

The product of its digits is 480, while the sum is 23.

The square root of 81351221 is about 9019.4911719010. The cubic root of 81351221 is about 433.2993377012.

Adding to 81351221 its reverse (12215318), we get a palindrome (93566539).

The spelling of 81351221 in words is "eighty-one million, three hundred fifty-one thousand, two hundred twenty-one".