81204521 has 2 divisors, whose sum is σ = 81204522. Its totient is φ = 81204520.

The previous prime is 81204493. The next prime is 81204527. The reversal of 81204521 is 12540218.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 81198121 + 6400 = 9011^2 + 80^2 .

It is a cyclic number.

It is not a de Polignac number, because 81204521 - 2⁶ = 81204457 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (81204527) 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 as a sum of consecutive naturals, namely, 40602260 + 40602261.

It is an arithmetic number, because the mean of its divisors is an integer number (40602261).

Almost surely, 2^81204521 is an apocalyptic number.

It is an amenable number.

81204521 is a deficient number, since it is larger than the sum of its proper divisors (1).

81204521 is an equidigital number, since it uses as much as digits as its factorization.

81204521 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 640, while the sum is 23.

The square root of 81204521 is about 9011.3551145208. The cubic root of 81204521 is about 433.0387259196.

Adding to 81204521 its reverse (12540218), we get a palindrome (93744739).

The spelling of 81204521 in words is "eighty-one million, two hundred four thousand, five hundred twenty-one".