81689477 has 2 divisors, whose sum is σ = 81689478. Its totient is φ = 81689476.

The previous prime is 81689473. The next prime is 81689479. The reversal of 81689477 is 77498618.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 80174116 + 1515361 = 8954^2 + 1231^2 .

It is a cyclic number.

It is not a de Polignac number, because 81689477 - 2² = 81689473 is a prime.

Together with 81689479, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81689473) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40844738 + 40844739.

It is an arithmetic number, because the mean of its divisors is an integer number (40844739).

Almost surely, 2^81689477 is an apocalyptic number.

It is an amenable number.

81689477 is a deficient number, since it is larger than the sum of its proper divisors (1).

81689477 is an equidigital number, since it uses as much as digits as its factorization.

81689477 is an evil number, because the sum of its binary digits is even.

The product of its digits is 677376, while the sum is 50.

The square root of 81689477 is about 9038.2231107669. The cubic root of 81689477 is about 433.8990559261.

The spelling of 81689477 in words is "eighty-one million, six hundred eighty-nine thousand, four hundred seventy-seven".