81990144 has 120 divisors (see below), whose sum is σ = 245765520. Its totient is φ = 27288576.

The previous prime is 81990143. The next prime is 81990151. The reversal of 81990144 is 44109918.

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 = 81990099 and 81990108.

It is not an unprimeable number, because it can be changed into a prime (81990143) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 124087 + ... + 124745.

It is an arithmetic number, because the mean of its divisors is an integer number (2048046).

Almost surely, 2^81990144 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 81990144, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (122882760).

81990144 is an abundant number, since it is smaller than the sum of its proper divisors (163775376).

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

81990144 is an frugal number, since it uses more digits than its factorization.

81990144 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 692 (or 664 counting only the distinct ones).

The product of its (nonzero) digits is 10368, while the sum is 36.

The square root of 81990144 is about 9054.8409152232. The cubic root of 81990144 is about 434.4307416967.

The spelling of 81990144 in words is "eighty-one million, nine hundred ninety thousand, one hundred forty-four".