81821925 has 72 divisors (see below), whose sum is σ = 155448384. Its totient is φ = 41057280.

The previous prime is 81821921. The next prime is 81821951. The reversal of 81821925 is 52912818.

It is not a de Polignac number, because 81821925 - 2² = 81821921 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81821925.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81821921) by changing a digit.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 501894 + ... + 502056.

Almost surely, 2^81821925 is an apocalyptic number.

It is an amenable number.

81821925 is a deficient number, since it is larger than the sum of its proper divisors (73626459).

81821925 is a wasteful number, since it uses less digits than its factorization.

81821925 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 299 (or 291 counting only the distinct ones).

The product of its digits is 11520, while the sum is 36.

The square root of 81821925 is about 9045.5472471266. The cubic root of 81821925 is about 434.1334314045.

The spelling of 81821925 in words is "eighty-one million, eight hundred twenty-one thousand, nine hundred twenty-five".