81661366 has 4 divisors (see below), whose sum is σ = 122492052. Its totient is φ = 40830682.

The previous prime is 81661301. The next prime is 81661379. The reversal of 81661366 is 66316618.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 66316618 = 2 ⋅33158309.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20415340 + ... + 20415343.

It is an arithmetic number, because the mean of its divisors is an integer number (30623013).

Almost surely, 2^81661366 is an apocalyptic number.

81661366 is a deficient number, since it is larger than the sum of its proper divisors (40830686).

81661366 is a wasteful number, since it uses less digits than its factorization.

81661366 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40830685.

The product of its digits is 31104, while the sum is 37.

The square root of 81661366 is about 9036.6678593384. The cubic root of 81661366 is about 433.8492790711.

The spelling of 81661366 in words is "eighty-one million, six hundred sixty-one thousand, three hundred sixty-six".