81205440 has 56 divisors (see below), whose sum is σ = 257830320. Its totient is φ = 21654528.

The previous prime is 81205429. The next prime is 81205489. The reversal of 81205440 is 4450218.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a self number, because there is not a number n which added to its sum of digits gives 81205440.

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 41335 + ... + 43254.

Almost surely, 2^81205440 is an apocalyptic number.

81205440 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81205440 is an abundant number, since it is smaller than the sum of its proper divisors (176624880).

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

81205440 is a wasteful number, since it uses less digits than its factorization.

81205440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 84609 (or 84599 counting only the distinct ones).

The product of its (nonzero) digits is 1280, while the sum is 24.

The square root of 81205440 is about 9011.4061055975. The cubic root of 81205440 is about 433.0403594949.

Adding to 81205440 its reverse (4450218), we get a palindrome (85655658).

The spelling of 81205440 in words is "eighty-one million, two hundred five thousand, four hundred forty".