81686621 has 16 divisors (see below), whose sum is σ = 85691520. Its totient is φ = 77812800.

The previous prime is 81686617. The next prime is 81686651. The reversal of 81686621 is 12668618.

It is a cyclic number.

It is not a de Polignac number, because 81686621 - 2² = 81686617 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81686651) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 472091 + ... + 472263.

It is an arithmetic number, because the mean of its divisors is an integer number (5355720).

Almost surely, 2^81686621 is an apocalyptic number.

It is an amenable number.

81686621 is a deficient number, since it is larger than the sum of its proper divisors (4004899).

81686621 is a wasteful number, since it uses less digits than its factorization.

81686621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 436.

The product of its digits is 27648, while the sum is 38.

The square root of 81686621 is about 9038.0651137287. The cubic root of 81686621 is about 433.8939992562.

The spelling of 81686621 in words is "eighty-one million, six hundred eighty-six thousand, six hundred twenty-one".