81205231 has 2 divisors, whose sum is σ = 81205232. Its totient is φ = 81205230.

The previous prime is 81205211. The next prime is 81205247. The reversal of 81205231 is 13250218.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81205231 - 2⁹ = 81204719 is a prime.

It is a super-3 number, since 3×81205231³ (a number of 25 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81205211) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40602615 + 40602616.

It is an arithmetic number, because the mean of its divisors is an integer number (40602616).

Almost surely, 2^81205231 is an apocalyptic number.

81205231 is a deficient number, since it is larger than the sum of its proper divisors (1).

81205231 is an equidigital number, since it uses as much as digits as its factorization.

81205231 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 480, while the sum is 22.

The square root of 81205231 is about 9011.3945091756. The cubic root of 81205231 is about 433.0399879865.

Adding to 81205231 its reverse (13250218), we get a palindrome (94455449).

The spelling of 81205231 in words is "eighty-one million, two hundred five thousand, two hundred thirty-one".