81505381 has 2 divisors, whose sum is σ = 81505382. Its totient is φ = 81505380.

The previous prime is 81505367. The next prime is 81505387. The reversal of 81505381 is 18350518.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 81450625 + 54756 = 9025^2 + 234^2 .

It is a cyclic number.

It is not a de Polignac number, because 81505381 - 2¹⁵ = 81472613 is a prime.

It is a super-2 number, since 2×81505381² = 13286254263910322, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81505387) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40752690 + 40752691.

It is an arithmetic number, because the mean of its divisors is an integer number (40752691).

Almost surely, 2^81505381 is an apocalyptic number.

It is an amenable number.

81505381 is a deficient number, since it is larger than the sum of its proper divisors (1).

81505381 is an equidigital number, since it uses as much as digits as its factorization.

81505381 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4800, while the sum is 31.

The square root of 81505381 is about 9028.0330637410. The cubic root of 81505381 is about 433.5728647440.

Adding to 81505381 its reverse (18350518), we get a palindrome (99855899).

It can be divided in two parts, 8150 and 5381, that added together give a palindrome (13531).

The spelling of 81505381 in words is "eighty-one million, five hundred five thousand, three hundred eighty-one".