81752221 has 2 divisors, whose sum is σ = 81752222. Its totient is φ = 81752220.

The previous prime is 81752219. The next prime is 81752243. The reversal of 81752221 is 12225718.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 43744996 + 38007225 = 6614^2 + 6165^2 .

It is a cyclic number.

It is not a de Polignac number, because 81752221 - 2¹ = 81752219 is a prime.

Together with 81752219, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 81752221.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81752521) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40876110 + 40876111.

It is an arithmetic number, because the mean of its divisors is an integer number (40876111).

Almost surely, 2^81752221 is an apocalyptic number.

It is an amenable number.

81752221 is a deficient number, since it is larger than the sum of its proper divisors (1).

81752221 is an equidigital number, since it uses as much as digits as its factorization.

81752221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2240, while the sum is 28.

The square root of 81752221 is about 9041.6934807590. The cubic root of 81752221 is about 434.0101171306.

Adding to 81752221 its reverse (12225718), we get a palindrome (93977939).

The spelling of 81752221 in words is "eighty-one million, seven hundred fifty-two thousand, two hundred twenty-one".