81220591 has 2 divisors, whose sum is σ = 81220592. Its totient is φ = 81220590.

The previous prime is 81220553. The next prime is 81220609. The reversal of 81220591 is 19502218.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81220591 - 2¹³ = 81212399 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81220541) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40610295 + 40610296.

It is an arithmetic number, because the mean of its divisors is an integer number (40610296).

Almost surely, 2^81220591 is an apocalyptic number.

81220591 is a deficient number, since it is larger than the sum of its proper divisors (1).

81220591 is an equidigital number, since it uses as much as digits as its factorization.

81220591 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1440, while the sum is 28.

The square root of 81220591 is about 9012.2467232095. The cubic root of 81220591 is about 433.0672894907.

The spelling of 81220591 in words is "eighty-one million, two hundred twenty thousand, five hundred ninety-one".