81664925 has 6 divisors (see below), whose sum is σ = 101264538. Its totient is φ = 65331920.

The previous prime is 81664901. The next prime is 81664949. The reversal of 81664925 is 52946618.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (81664901) and next prime (81664949).

It can be written as a sum of positive squares in 3 ways, for example, as 196249 + 81468676 = 443^2 + 9026^2 .

It is not a de Polignac number, because 81664925 - 2²² = 77470621 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1633274 + ... + 1633323.

It is an arithmetic number, because the mean of its divisors is an integer number (16877423).

Almost surely, 2^81664925 is an apocalyptic number.

It is an amenable number.

81664925 is a deficient number, since it is larger than the sum of its proper divisors (19599613).

81664925 is a wasteful number, since it uses less digits than its factorization.

81664925 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3266607 (or 3266602 counting only the distinct ones).

The product of its digits is 103680, while the sum is 41.

The square root of 81664925 is about 9036.8647771226. The cubic root of 81664925 is about 433.8555817135.

The spelling of 81664925 in words is "eighty-one million, six hundred sixty-four thousand, nine hundred twenty-five".