81581661620 has 12 divisors (see below), whose sum is σ = 171321489444. Its totient is φ = 32632664640.

The previous prime is 81581661617. The next prime is 81581661661. The reversal of 81581661620 is 2616618518.

It can be written as a sum of positive squares in 2 ways, for example, as 43175852944 + 38405808676 = 207788^2 + 195974^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2039541521 + ... + 2039541560.

It is an arithmetic number, because the mean of its divisors is an integer number (14276790787).

Almost surely, 2^81581661620 is an apocalyptic number.

It is an amenable number.

81581661620 is an abundant number, since it is smaller than the sum of its proper divisors (89739827824).

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

81581661620 is a wasteful number, since it uses less digits than its factorization.

81581661620 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4079083090 (or 4079083088 counting only the distinct ones).

The product of its (nonzero) digits is 138240, while the sum is 44.

The spelling of 81581661620 in words is "eighty-one billion, five hundred eighty-one million, six hundred sixty-one thousand, six hundred twenty".