81640489984 has 33 divisors (see below), whose sum is σ = 163219532637. Its totient is φ = 40815673344.

The previous prime is 81640489979. The next prime is 81640489993. The reversal of 81640489984 is 48998404618.

The square root of 81640489984 is 285728.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 3061187584 + 78579302400 = 55328^2 + 280320^2 .

It is a super-4 number, since 4×81640489984⁴ (a number of 45 digits) contains 4444 as substring.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 9138832 + ... + 9147760.

Almost surely, 2^81640489984 is an apocalyptic number.

81640489984 is the 285728-th square number.

It is an amenable number.

81640489984 is a deficient number, since it is larger than the sum of its proper divisors (81579042653).

81640489984 is an frugal number, since it uses more digits than its factorization.

81640489984 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17878 (or 8931 counting only the distinct ones).

The product of its (nonzero) digits is 15925248, while the sum is 61.

The spelling of 81640489984 in words is "eighty-one billion, six hundred forty million, four hundred eighty-nine thousand, nine hundred eighty-four".