81366521 has 2 divisors, whose sum is σ = 81366522. Its totient is φ = 81366520.

The previous prime is 81366491. The next prime is 81366533. The reversal of 81366521 is 12566318.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 74580496 + 6786025 = 8636^2 + 2605^2 .

It is a cyclic number.

It is not a de Polignac number, because 81366521 - 2¹⁸ = 81104377 is a prime.

It is not a weakly prime, because it can be changed into another prime (81366121) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40683260 + 40683261.

It is an arithmetic number, because the mean of its divisors is an integer number (40683261).

Almost surely, 2^81366521 is an apocalyptic number.

It is an amenable number.

81366521 is a deficient number, since it is larger than the sum of its proper divisors (1).

81366521 is an equidigital number, since it uses as much as digits as its factorization.

81366521 is an evil number, because the sum of its binary digits is even.

The product of its digits is 8640, while the sum is 32.

The square root of 81366521 is about 9020.3392951707. The cubic root of 81366521 is about 433.3265000237.

The spelling of 81366521 in words is "eighty-one million, three hundred sixty-six thousand, five hundred twenty-one".