81297780 has 96 divisors (see below), whose sum is σ = 235339776. Its totient is φ = 20958336.

The previous prime is 81297761. The next prime is 81297781. The reversal of 81297780 is 8779218.

It is a hoax number, since the sum of its digits (42) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81297781) 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 31 ways as a sum of consecutive naturals, for example, 358027 + ... + 358253.

It is an arithmetic number, because the mean of its divisors is an integer number (2451456).

Almost surely, 2^81297780 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 81297780, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (117669888).

81297780 is an abundant number, since it is smaller than the sum of its proper divisors (154041996).

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

81297780 is a wasteful number, since it uses less digits than its factorization.

81297780 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 413 (or 411 counting only the distinct ones).

The product of its (nonzero) digits is 56448, while the sum is 42.

The square root of 81297780 is about 9016.5281566687. The cubic root of 81297780 is about 433.2044363505.

The spelling of 81297780 in words is "eighty-one million, two hundred ninety-seven thousand, seven hundred eighty".