81705511 has 2 divisors, whose sum is σ = 81705512. Its totient is φ = 81705510.

The previous prime is 81705487. The next prime is 81705517. The reversal of 81705511 is 11550718.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81705511 - 2⁵ = 81705479 is a prime.

It is a super-2 number, since 2×81705511² = 13351581055542242, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 81705511.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81705517) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40852755 + 40852756.

It is an arithmetic number, because the mean of its divisors is an integer number (40852756).

Almost surely, 2^81705511 is an apocalyptic number.

81705511 is a deficient number, since it is larger than the sum of its proper divisors (1).

81705511 is an equidigital number, since it uses as much as digits as its factorization.

81705511 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1400, while the sum is 28.

The square root of 81705511 is about 9039.1100778782. The cubic root of 81705511 is about 433.9274426191.

The spelling of 81705511 in words is "eighty-one million, seven hundred five thousand, five hundred eleven".