81256720 has 20 divisors (see below), whose sum is σ = 188922060. Its totient is φ = 32502656.

The previous prime is 81256691. The next prime is 81256727. The reversal of 81256720 is 2765218.

It can be written as a sum of positive squares in 2 ways, for example, as 40347904 + 40908816 = 6352^2 + 6396^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is not an unprimeable number, because it can be changed into a prime (81256727) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 507775 + ... + 507934.

It is an arithmetic number, because the mean of its divisors is an integer number (9446103).

Almost surely, 2^81256720 is an apocalyptic number.

81256720 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81256720 is an abundant number, since it is smaller than the sum of its proper divisors (107665340).

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

81256720 is a wasteful number, since it uses less digits than its factorization.

81256720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1015722 (or 1015716 counting only the distinct ones).

The product of its (nonzero) digits is 6720, while the sum is 31.

The square root of 81256720 is about 9014.2509394847. The cubic root of 81256720 is about 433.1314931142.

The spelling of 81256720 in words is "eighty-one million, two hundred fifty-six thousand, seven hundred twenty".