81161221 has 2 divisors, whose sum is σ = 81161222. Its totient is φ = 81161220.

The previous prime is 81161209. The next prime is 81161231. The reversal of 81161221 is 12216118.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 72488196 + 8673025 = 8514^2 + 2945^2 .

It is a cyclic number.

It is not a de Polignac number, because 81161221 - 2⁵ = 81161189 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 81161192 and 81161201.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81161231) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40580610 + 40580611.

It is an arithmetic number, because the mean of its divisors is an integer number (40580611).

Almost surely, 2^81161221 is an apocalyptic number.

It is an amenable number.

81161221 is a deficient number, since it is larger than the sum of its proper divisors (1).

81161221 is an equidigital number, since it uses as much as digits as its factorization.

81161221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 192, while the sum is 22.

The square root of 81161221 is about 9008.9522698258. The cubic root of 81161221 is about 432.9617437093.

Adding to 81161221 its reverse (12216118), we get a palindrome (93377339).

The spelling of 81161221 in words is "eighty-one million, one hundred sixty-one thousand, two hundred twenty-one".