81890640 has 180 divisors, whose sum is σ = 298240956. Its totient is φ = 20127744.

The previous prime is 81890587. The next prime is 81890647. The reversal of 81890640 is 4609818.

It is a happy number.

81890640 is a `hidden beast` number, since 8 + 1 + 8 + 9 + 0 + 640 = 666.

It can be written as a sum of positive squares in 6 ways, for example, as 22353984 + 59536656 = 4728^2 + 7716^2 .

It is a tau number, because it is divible by the number of its divisors (180).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 81890595 and 81890604.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81890647) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 121344 + ... + 122016.

Almost surely, 2^81890640 is an apocalyptic number.

81890640 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81890640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (149120478).

81890640 is an abundant number, since it is smaller than the sum of its proper divisors (216350316).

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

81890640 is a wasteful number, since it uses less digits than its factorization.

81890640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 718 (or 696 counting only the distinct ones).

The product of its (nonzero) digits is 13824, while the sum is 36.

The square root of 81890640 is about 9049.3447276585. The cubic root of 81890640 is about 434.2549274937.

The spelling of 81890640 in words is "eighty-one million, eight hundred ninety thousand, six hundred forty".