81856661 has 2 divisors, whose sum is σ = 81856662. Its totient is φ = 81856660.

The previous prime is 81856603. The next prime is 81856703. The reversal of 81856661 is 16665818.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 77880625 + 3976036 = 8825^2 + 1994^2 .

It is a cyclic number.

It is not a de Polignac number, because 81856661 - 2¹⁸ = 81594517 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81856361) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40928330 + 40928331.

It is an arithmetic number, because the mean of its divisors is an integer number (40928331).

Almost surely, 2^81856661 is an apocalyptic number.

It is an amenable number.

81856661 is a deficient number, since it is larger than the sum of its proper divisors (1).

81856661 is an equidigital number, since it uses as much as digits as its factorization.

81856661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 69120, while the sum is 41.

The square root of 81856661 is about 9047.4671041126. The cubic root of 81856661 is about 434.1948571792.

The spelling of 81856661 in words is "eighty-one million, eight hundred fifty-six thousand, six hundred sixty-one".