81643221 has 20 divisors (see below), whose sum is σ = 133049664. Its totient is φ = 49480200.

The previous prime is 81643217. The next prime is 81643229. The reversal of 81643221 is 12234618.

It is not a de Polignac number, because 81643221 - 2² = 81643217 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81643229) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 44925 + ... + 46706.

Almost surely, 2^81643221 is an apocalyptic number.

81643221 is a gapful number since it is divisible by the number (81) formed by its first and last digit.

It is an amenable number.

81643221 is a deficient number, since it is larger than the sum of its proper divisors (51406443).

81643221 is a wasteful number, since it uses less digits than its factorization.

81643221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 91654 (or 91645 counting only the distinct ones).

The product of its digits is 2304, while the sum is 27.

The square root of 81643221 is about 9035.6638383685. The cubic root of 81643221 is about 433.8171431963.

Adding to 81643221 its reverse (12234618), we get a palindrome (93877839).

The spelling of 81643221 in words is "eighty-one million, six hundred forty-three thousand, two hundred twenty-one".