81720427 has 2 divisors, whose sum is σ = 81720428. Its totient is φ = 81720426.

The previous prime is 81720409. The next prime is 81720437. The reversal of 81720427 is 72402718.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81720427 - 2⁷ = 81720299 is a prime.

It is not a weakly prime, because it can be changed into another prime (81720437) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40860213 + 40860214.

It is an arithmetic number, because the mean of its divisors is an integer number (40860214).

Almost surely, 2^81720427 is an apocalyptic number.

81720427 is a deficient number, since it is larger than the sum of its proper divisors (1).

81720427 is an equidigital number, since it uses as much as digits as its factorization.

81720427 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 6272, while the sum is 31.

The square root of 81720427 is about 9039.9351214486. The cubic root of 81720427 is about 433.9538466639.

The spelling of 81720427 in words is "eighty-one million, seven hundred twenty thousand, four hundred twenty-seven".