81308221 has 2 divisors, whose sum is σ = 81308222. Its totient is φ = 81308220.

The previous prime is 81308191. The next prime is 81308231. The reversal of 81308221 is 12280318.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 77264100 + 4044121 = 8790^2 + 2011^2 .

It is a cyclic number.

It is not a de Polignac number, because 81308221 - 2¹³ = 81300029 is a prime.

It is a super-2 number, since 2×81308221² = 13222053604369682, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81308231) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40654110 + 40654111.

It is an arithmetic number, because the mean of its divisors is an integer number (40654111).

Almost surely, 2^81308221 is an apocalyptic number.

It is an amenable number.

81308221 is a deficient number, since it is larger than the sum of its proper divisors (1).

81308221 is an equidigital number, since it uses as much as digits as its factorization.

81308221 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 768, while the sum is 25.

The square root of 81308221 is about 9017.1071303384. The cubic root of 81308221 is about 433.2229809073. Note that the first 3 decimals are identical.

Adding to 81308221 its reverse (12280318), we get a palindrome (93588539).

The spelling of 81308221 in words is "eighty-one million, three hundred eight thousand, two hundred twenty-one".