81666620 has 48 divisors (see below), whose sum is σ = 199342080. Its totient is φ = 27522624.

The previous prime is 81666619. The next prime is 81666631. The reversal of 81666620 is 2666618.

It is a Harshad number since it is a multiple of its sum of digits (35).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3317 + ... + 13203.

It is an arithmetic number, because the mean of its divisors is an integer number (4152960).

Almost surely, 2^81666620 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81666620, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (99671040).

81666620 is an abundant number, since it is smaller than the sum of its proper divisors (117675460).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81666620 is a wasteful number, since it uses less digits than its factorization.

81666620 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9962 (or 9960 counting only the distinct ones).

The product of its (nonzero) digits is 20736, while the sum is 35.

The square root of 81666620 is about 9036.9585591614. The cubic root of 81666620 is about 433.8585833290.

81666620 divided by its sum of digits (35) gives a palindrome (2333332).

The spelling of 81666620 in words is "eighty-one million, six hundred sixty-six thousand, six hundred twenty".