81515520 has 264 divisors, whose sum is σ = 296978760. Its totient is φ = 20643840.

The previous prime is 81515479. The next prime is 81515579. The reversal of 81515520 is 2551518.

It can be written as a sum of positive squares in 4 ways, for example, as 82944 + 81432576 = 288^2 + 9024^2 .

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1336290 + ... + 1336350.

Almost surely, 2^81515520 is an apocalyptic number.

81515520 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 81515520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (148489380).

81515520 is an abundant number, since it is smaller than the sum of its proper divisors (215463240).

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

81515520 is a wasteful number, since it uses less digits than its factorization.

81515520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 121 (or 100 counting only the distinct ones).

The product of its (nonzero) digits is 2000, while the sum is 27.

The square root of 81515520 is about 9028.5945750155. The cubic root of 81515520 is about 433.5908423423.

The spelling of 81515520 in words is "eighty-one million, five hundred fifteen thousand, five hundred twenty".