81806621 has 4 divisors (see below), whose sum is σ = 88099452. Its totient is φ = 75513792.

The previous prime is 81806611. The next prime is 81806639. The reversal of 81806621 is 12660818.

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

It can be written as a sum of positive squares in 2 ways, for example, as 51984100 + 29822521 = 7210^2 + 5461^2 .

It is a cyclic number.

It is not a de Polignac number, because 81806621 - 2²⁶ = 14697757 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 (81806611) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3146396 + ... + 3146421.

It is an arithmetic number, because the mean of its divisors is an integer number (22024863).

Almost surely, 2^81806621 is an apocalyptic number.

It is an amenable number.

81806621 is a deficient number, since it is larger than the sum of its proper divisors (6292831).

81806621 is a wasteful number, since it uses less digits than its factorization.

81806621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6292830.

The product of its (nonzero) digits is 4608, while the sum is 32.

The square root of 81806621 is about 9044.7012664875. The cubic root of 81806621 is about 434.1063628965.

The spelling of 81806621 in words is "eighty-one million, eight hundred six thousand, six hundred twenty-one".