81888221 has 2 divisors, whose sum is σ = 81888222. Its totient is φ = 81888220.

The previous prime is 81888197. The next prime is 81888223. The reversal of 81888221 is 12288818.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 59892121 + 21996100 = 7739^2 + 4690^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81888221 is a prime.

Together with 81888223, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81888223) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40944110 + 40944111.

It is an arithmetic number, because the mean of its divisors is an integer number (40944111).

Almost surely, 2^81888221 is an apocalyptic number.

It is an amenable number.

81888221 is a deficient number, since it is larger than the sum of its proper divisors (1).

81888221 is an equidigital number, since it uses as much as digits as its factorization.

81888221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 16384, while the sum is 38.

The square root of 81888221 is about 9049.2110705851. The cubic root of 81888221 is about 434.2506515756.

The spelling of 81888221 in words is "eighty-one million, eight hundred eighty-eight thousand, two hundred twenty-one".