81778720 has 48 divisors (see below), whose sum is σ = 196499520. Its totient is φ = 32153344.

The previous prime is 81778703. The next prime is 81778757. The reversal of 81778720 is 2787718.

81778720 = T₄₉₅ + T₄₉₆ + ... + T₈₄₈.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (40).

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 7 ways as a sum of consecutive naturals, for example, 5109 + ... + 13771.

It is an arithmetic number, because the mean of its divisors is an integer number (4093740).

Almost surely, 2^81778720 is an apocalyptic number.

81778720 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 81778720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (98249760).

81778720 is an abundant number, since it is smaller than the sum of its proper divisors (114720800).

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

81778720 is a wasteful number, since it uses less digits than its factorization.

81778720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8737 (or 8729 counting only the distinct ones).

The product of its (nonzero) digits is 43904, while the sum is 40.

The square root of 81778720 is about 9043.1587401748. The cubic root of 81778720 is about 434.0570051195.

The spelling of 81778720 in words is "eighty-one million, seven hundred seventy-eight thousand, seven hundred twenty".