81651780 has 96 divisors (see below), whose sum is σ = 290330880. Its totient is φ = 18662400.

The previous prime is 81651767. The next prime is 81651809. The reversal of 81651780 is 8715618.

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

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 31 ways as a sum of consecutive naturals, for example, 7021 + ... + 14580.

It is an arithmetic number, because the mean of its divisors is an integer number (3024280).

Almost surely, 2^81651780 is an apocalyptic number.

It is an amenable number.

81651780 is an abundant number, since it is smaller than the sum of its proper divisors (208679100).

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

81651780 is a wasteful number, since it uses less digits than its factorization.

81651780 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21626 (or 21618 counting only the distinct ones).

The product of its (nonzero) digits is 13440, while the sum is 36.

The square root of 81651780 is about 9036.1374491538. The cubic root of 81651780 is about 433.8323022879.

The spelling of 81651780 in words is "eighty-one million, six hundred fifty-one thousand, seven hundred eighty".