81787680 has 288 divisors, whose sum is σ = 319488624. Its totient is φ = 18874368.

The previous prime is 81787633. The next prime is 81787681. The reversal of 81787680 is 8678718.

It can be written as a sum of positive squares in 8 ways, for example, as 57699216 + 24088464 = 7596^2 + 4908^2 .

It is a tau number, because it is divible by the number of its divisors (288).

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

It is not an unprimeable number, because it can be changed into a prime (81787681) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 318112 + ... + 318368.

Almost surely, 2^81787680 is an apocalyptic number.

81787680 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 81787680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (159744312).

81787680 is an abundant number, since it is smaller than the sum of its proper divisors (237700944).

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

81787680 is a wasteful number, since it uses less digits than its factorization.

81787680 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 308 (or 297 counting only the distinct ones).

The product of its (nonzero) digits is 150528, while the sum is 45.

The square root of 81787680 is about 9043.6541287247. The cubic root of 81787680 is about 434.0728568746.

The spelling of 81787680 in words is "eighty-one million, seven hundred eighty-seven thousand, six hundred eighty".