81761771520 has 1344 divisors, whose sum is σ = 351419281920. Its totient is φ = 17907056640.

The previous prime is 81761771519. The next prime is 81761771549. The reversal of 81761771520 is 2517716718.

81761771520 is a `hidden beast` number, since 8 + 1 + 7 + 617 + 7 + 1 + 5 + 20 = 666.

It is a super-2 number, since 2×81761771520² (a number of 23 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 1739612137 + ... + 1739612183.

It is an arithmetic number, because the mean of its divisors is an integer number (261472680).

Almost surely, 2^81761771520 is an apocalyptic number.

81761771520 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 81761771520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (175709640960).

81761771520 is an abundant number, since it is smaller than the sum of its proper divisors (269657510400).

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

81761771520 is a wasteful number, since it uses less digits than its factorization.

81761771520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 122 (or 81 counting only the distinct ones).

The product of its (nonzero) digits is 164640, while the sum is 45.

The spelling of 81761771520 in words is "eighty-one billion, seven hundred sixty-one million, seven hundred seventy-one thousand, five hundred twenty".