81604321 has 2 divisors, whose sum is σ = 81604322. Its totient is φ = 81604320.

The previous prime is 81604279. The next prime is 81604331. The reversal of 81604321 is 12340618.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 69072721 + 12531600 = 8311^2 + 3540^2 .

It is a cyclic number.

It is not a de Polignac number, because 81604321 - 2¹¹ = 81602273 is a prime.

It is not a weakly prime, because it can be changed into another prime (81604331) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40802160 + 40802161.

It is an arithmetic number, because the mean of its divisors is an integer number (40802161).

Almost surely, 2^81604321 is an apocalyptic number.

81604321 is the 5216-th hex number.

It is an amenable number.

81604321 is a deficient number, since it is larger than the sum of its proper divisors (1).

81604321 is an equidigital number, since it uses as much as digits as its factorization.

81604321 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1152, while the sum is 25.

The square root of 81604321 is about 9033.5110007128. The cubic root of 81604321 is about 433.7482329322.

Adding to 81604321 its reverse (12340618), we get a palindrome (93944939).

The spelling of 81604321 in words is "eighty-one million, six hundred four thousand, three hundred twenty-one".