81987811 has 2 divisors, whose sum is σ = 81987812. Its totient is φ = 81987810.

The previous prime is 81987809. The next prime is 81987817. The reversal of 81987811 is 11878918.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81987811 - 2¹ = 81987809 is a prime.

Together with 81987809, it forms a pair of twin primes.

It is equal to p_4778737 and since 81987811 and 4778737 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (81987817) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40993905 + 40993906.

It is an arithmetic number, because the mean of its divisors is an integer number (40993906).

Almost surely, 2^81987811 is an apocalyptic number.

81987811 is a deficient number, since it is larger than the sum of its proper divisors (1).

81987811 is an equidigital number, since it uses as much as digits as its factorization.

81987811 is an evil number, because the sum of its binary digits is even.

The product of its digits is 32256, while the sum is 43.

The square root of 81987811 is about 9054.7120881892. The cubic root of 81987811 is about 434.4266211342.

The spelling of 81987811 in words is "eighty-one million, nine hundred eighty-seven thousand, eight hundred eleven".