81561123840 has 352 divisors, whose sum is σ = 299106984960. Its totient is φ = 18581815296.

The previous prime is 81561123817. The next prime is 81561123893. The reversal of 81561123840 is 4832116518.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 38598624 + ... + 38600736.

Almost surely, 2^81561123840 is an apocalyptic number.

81561123840 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81561123840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (149553492480).

81561123840 is an abundant number, since it is smaller than the sum of its proper divisors (217545861120).

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

81561123840 is a wasteful number, since it uses less digits than its factorization.

81561123840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2507 (or 2489 counting only the distinct ones).

The product of its (nonzero) digits is 46080, while the sum is 39.

The spelling of 81561123840 in words is "eighty-one billion, five hundred sixty-one million, one hundred twenty-three thousand, eight hundred forty".