81221075447 has 2 divisors, whose sum is σ = 81221075448. Its totient is φ = 81221075446.

The previous prime is 81221075371. The next prime is 81221075449. The reversal of 81221075447 is 74457012218.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81221075447 - 2¹⁰ = 81221074423 is a prime.

Together with 81221075449, 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 (81221075449) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40610537723 + 40610537724.

It is an arithmetic number, because the mean of its divisors is an integer number (40610537724).

Almost surely, 2^81221075447 is an apocalyptic number.

81221075447 is a deficient number, since it is larger than the sum of its proper divisors (1).

81221075447 is an equidigital number, since it uses as much as digits as its factorization.

81221075447 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 125440, while the sum is 41.

The spelling of 81221075447 in words is "eighty-one billion, two hundred twenty-one million, seventy-five thousand, four hundred forty-seven".