81685890 has 144 divisors (see below), whose sum is σ = 251839224. Its totient is φ = 18247680.

The previous prime is 81685841. The next prime is 81685937. The reversal of 81685890 is 9858618.

81685890 is a `hidden beast` number, since 8 + 1 + 68 + 589 + 0 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 74183769 + 7502121 = 8613^2 + 2739^2 .

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 141282 + ... + 141858.

Almost surely, 2^81685890 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81685890, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (125919612).

81685890 is an abundant number, since it is smaller than the sum of its proper divisors (170153334).

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

81685890 is a wasteful number, since it uses less digits than its factorization.

81685890 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 625 (or 611 counting only the distinct ones).

The product of its (nonzero) digits is 138240, while the sum is 45.

The square root of 81685890 is about 9038.0246735667. The cubic root of 81685890 is about 433.8927049706.

The spelling of 81685890 in words is "eighty-one million, six hundred eighty-five thousand, eight hundred ninety".