81392221 has 2 divisors, whose sum is σ = 81392222. Its totient is φ = 81392220.

The previous prime is 81392161. The next prime is 81392251. The reversal of 81392221 is 12229318.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 77686596 + 3705625 = 8814^2 + 1925^2 .

It is a cyclic number.

It is not a de Polignac number, because 81392221 - 2¹¹ = 81390173 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81392221.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81392251) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40696110 + 40696111.

It is an arithmetic number, because the mean of its divisors is an integer number (40696111).

Almost surely, 2^81392221 is an apocalyptic number.

It is an amenable number.

81392221 is a deficient number, since it is larger than the sum of its proper divisors (1).

81392221 is an equidigital number, since it uses as much as digits as its factorization.

81392221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1728, while the sum is 28.

The square root of 81392221 is about 9021.7637410874. The cubic root of 81392221 is about 433.3721179618.

The spelling of 81392221 in words is "eighty-one million, three hundred ninety-two thousand, two hundred twenty-one".