81224209 has 4 divisors (see below), whose sum is σ = 88608240. Its totient is φ = 73840180.

The previous prime is 81224197. The next prime is 81224237. The reversal of 81224209 is 90242218.

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.

It is a cyclic number.

It is not a de Polignac number, because 81224209 - 2⁵ = 81224177 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81224279) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3691999 + ... + 3692020.

It is an arithmetic number, because the mean of its divisors is an integer number (22152060).

Almost surely, 2^81224209 is an apocalyptic number.

It is an amenable number.

81224209 is a deficient number, since it is larger than the sum of its proper divisors (7384031).

81224209 is a wasteful number, since it uses less digits than its factorization.

81224209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7384030.

The product of its (nonzero) digits is 2304, while the sum is 28.

The square root of 81224209 is about 9012.4474478357. The cubic root of 81224209 is about 433.0737197739.

Subtracting 81224209 from its reverse (90242218), we obtain a square (9018009 = 3003²).

The spelling of 81224209 in words is "eighty-one million, two hundred twenty-four thousand, two hundred nine".