81688643 has 2 divisors, whose sum is σ = 81688644. Its totient is φ = 81688642.

The previous prime is 81688639. The next prime is 81688661. The reversal of 81688643 is 34688618.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81688643 - 2² = 81688639 is a prime.

It is a super-3 number, since 3×81688643³ (a number of 25 digits) contains 333 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 81688594 and 81688603.

It is not a weakly prime, because it can be changed into another prime (81688603) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40844321 + 40844322.

It is an arithmetic number, because the mean of its divisors is an integer number (40844322).

Almost surely, 2^81688643 is an apocalyptic number.

81688643 is a deficient number, since it is larger than the sum of its proper divisors (1).

81688643 is an equidigital number, since it uses as much as digits as its factorization.

81688643 is an evil number, because the sum of its binary digits is even.

The product of its digits is 221184, while the sum is 44.

The square root of 81688643 is about 9038.1769732618. The cubic root of 81688643 is about 433.8975793057.

The spelling of 81688643 in words is "eighty-one million, six hundred eighty-eight thousand, six hundred forty-three".