81643421 has 4 divisors (see below), whose sum is σ = 81871200. Its totient is φ = 81415644.

The previous prime is 81643379. The next prime is 81643427. The reversal of 81643421 is 12434618.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81643421 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 (81643427) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 113351 + ... + 114068.

It is an arithmetic number, because the mean of its divisors is an integer number (20467800).

Almost surely, 2^81643421 is an apocalyptic number.

It is an amenable number.

81643421 is a deficient number, since it is larger than the sum of its proper divisors (227779).

81643421 is a wasteful number, since it uses less digits than its factorization.

81643421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 227778.

The product of its digits is 4608, while the sum is 29.

The square root of 81643421 is about 9035.6749056172. The cubic root of 81643421 is about 433.8174974342.

The spelling of 81643421 in words is "eighty-one million, six hundred forty-three thousand, four hundred twenty-one".