81520643578 has 16 divisors (see below), whose sum is σ = 134371125504. Its totient is φ = 36784363360.

The previous prime is 81520643527. The next prime is 81520643587. The reversal of 81520643578 is 87534602518.

It is a happy number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 13520650 + ... + 13526677.

It is an arithmetic number, because the mean of its divisors is an integer number (8398195344).

Almost surely, 2^81520643578 is an apocalyptic number.

81520643578 is a deficient number, since it is larger than the sum of its proper divisors (52850481926).

81520643578 is a wasteful number, since it uses less digits than its factorization.

81520643578 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27047477.

The product of its (nonzero) digits is 1612800, while the sum is 49.

The spelling of 81520643578 in words is "eighty-one billion, five hundred twenty million, six hundred forty-three thousand, five hundred seventy-eight".