81786821 has 2 divisors, whose sum is σ = 81786822. Its totient is φ = 81786820.

The previous prime is 81786799. The next prime is 81786823. The reversal of 81786821 is 12868718.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 74822500 + 6964321 = 8650^2 + 2639^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81786821 is a prime.

Together with 81786823, 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 (81786823) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40893410 + 40893411.

It is an arithmetic number, because the mean of its divisors is an integer number (40893411).

Almost surely, 2^81786821 is an apocalyptic number.

It is an amenable number.

81786821 is a deficient number, since it is larger than the sum of its proper divisors (1).

81786821 is an equidigital number, since it uses as much as digits as its factorization.

81786821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 43008, while the sum is 41.

The square root of 81786821 is about 9043.6066367351. The cubic root of 81786821 is about 434.0713372086.

The spelling of 81786821 in words is "eighty-one million, seven hundred eighty-six thousand, eight hundred twenty-one".