81521025 has 24 divisors (see below), whose sum is σ = 135988320. Its totient is φ = 43088640.

The previous prime is 81521021. The next prime is 81521047. The reversal of 81521025 is 52012518.

It is not a de Polignac number, because 81521025 - 2² = 81521021 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 81520986 and 81521004.

It is not an unprimeable number, because it can be changed into a prime (81521021) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 3666 + ... + 13284.

It is an arithmetic number, because the mean of its divisors is an integer number (5666180).

Almost surely, 2^81521025 is an apocalyptic number.

It is an amenable number.

81521025 is a deficient number, since it is larger than the sum of its proper divisors (54467295).

81521025 is a wasteful number, since it uses less digits than its factorization.

81521025 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9745 (or 9740 counting only the distinct ones).

The product of its (nonzero) digits is 800, while the sum is 24.

The square root of 81521025 is about 9028.8994345933. The cubic root of 81521025 is about 433.6006027080.

The spelling of 81521025 in words is "eighty-one million, five hundred twenty-one thousand, twenty-five".