81639566 has 4 divisors (see below), whose sum is σ = 122459352. Its totient is φ = 40819782.

The previous prime is 81639527. The next prime is 81639587. The reversal of 81639566 is 66593618.

It is a semiprime because it is the product of two primes.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20409890 + ... + 20409893.

It is an arithmetic number, because the mean of its divisors is an integer number (30614838).

Almost surely, 2^81639566 is an apocalyptic number.

81639566 is a deficient number, since it is larger than the sum of its proper divisors (40819786).

81639566 is a wasteful number, since it uses less digits than its factorization.

81639566 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40819785.

The product of its digits is 233280, while the sum is 44.

The square root of 81639566 is about 9035.4615820112. The cubic root of 81639566 is about 433.8106693977.

The spelling of 81639566 in words is "eighty-one million, six hundred thirty-nine thousand, five hundred sixty-six".