81284221 has 2 divisors, whose sum is σ = 81284222. Its totient is φ = 81284220.

The previous prime is 81284219. The next prime is 81284257. The reversal of 81284221 is 12248218.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 72012196 + 9272025 = 8486^2 + 3045^2 .

It is a cyclic number.

It is not a de Polignac number, because 81284221 - 2¹ = 81284219 is a prime.

Together with 81284219, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 81284221.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81285221) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40642110 + 40642111.

It is an arithmetic number, because the mean of its divisors is an integer number (40642111).

Almost surely, 2^81284221 is an apocalyptic number.

It is an amenable number.

81284221 is a deficient number, since it is larger than the sum of its proper divisors (1).

81284221 is an equidigital number, since it uses as much as digits as its factorization.

81284221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2048, while the sum is 28.

The square root of 81284221 is about 9015.7762283677. The cubic root of 81284221 is about 433.1803514553.

The spelling of 81284221 in words is "eighty-one million, two hundred eighty-four thousand, two hundred twenty-one".