81556693 has 2 divisors, whose sum is σ = 81556694. Its totient is φ = 81556692.

The previous prime is 81556687. The next prime is 81556697. The reversal of 81556693 is 39665518.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 76440049 + 5116644 = 8743^2 + 2262^2 .

It is a cyclic number.

It is not a de Polignac number, because 81556693 - 2⁵ = 81556661 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81556697) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40778346 + 40778347.

It is an arithmetic number, because the mean of its divisors is an integer number (40778347).

Almost surely, 2^81556693 is an apocalyptic number.

It is an amenable number.

81556693 is a deficient number, since it is larger than the sum of its proper divisors (1).

81556693 is an equidigital number, since it uses as much as digits as its factorization.

81556693 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 194400, while the sum is 43.

The square root of 81556693 is about 9030.8744316373. The cubic root of 81556693 is about 433.6638314325.

The spelling of 81556693 in words is "eighty-one million, five hundred fifty-six thousand, six hundred ninety-three".