81639375 has 20 divisors (see below), whose sum is σ = 136025208. Its totient is φ = 43540000.

The previous prime is 81639367. The next prime is 81639407. The reversal of 81639375 is 57393618.

It is not a de Polignac number, because 81639375 - 2³ = 81639367 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 19896 + ... + 23645.

Almost surely, 2^81639375 is an apocalyptic number.

81639375 is a deficient number, since it is larger than the sum of its proper divisors (54385833).

81639375 is an equidigital number, since it uses as much as digits as its factorization.

81639375 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 43564 (or 43549 counting only the distinct ones).

The product of its digits is 136080, while the sum is 42.

The square root of 81639375 is about 9035.4510125394. The cubic root of 81639375 is about 433.8103310899.

The spelling of 81639375 in words is "eighty-one million, six hundred thirty-nine thousand, three hundred seventy-five".