81332821 has 2 divisors, whose sum is σ = 81332822. Its totient is φ = 81332820.

The previous prime is 81332813. The next prime is 81332827. The reversal of 81332821 is 12823318.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 62583921 + 18748900 = 7911^2 + 4330^2 .

It is a cyclic number.

It is not a de Polignac number, because 81332821 - 2³ = 81332813 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81332821.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81332827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40666410 + 40666411.

It is an arithmetic number, because the mean of its divisors is an integer number (40666411).

Almost surely, 2^81332821 is an apocalyptic number.

It is an amenable number.

81332821 is a deficient number, since it is larger than the sum of its proper divisors (1).

81332821 is an equidigital number, since it uses as much as digits as its factorization.

81332821 is an evil number, because the sum of its binary digits is even.

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

The square root of 81332821 is about 9018.4711010237. The cubic root of 81332821 is about 433.2666673906.

The spelling of 81332821 in words is "eighty-one million, three hundred thirty-two thousand, eight hundred twenty-one".