81181537 has 2 divisors, whose sum is σ = 81181538. Its totient is φ = 81181536.

The previous prime is 81181523. The next prime is 81181561. The reversal of 81181537 is 73518118.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 76055841 + 5125696 = 8721^2 + 2264^2 .

It is a cyclic number.

It is not a de Polignac number, because 81181537 - 2¹⁹ = 80657249 is a prime.

It is not a weakly prime, because it can be changed into another prime (81181567) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40590768 + 40590769.

It is an arithmetic number, because the mean of its divisors is an integer number (40590769).

Almost surely, 2^81181537 is an apocalyptic number.

It is an amenable number.

81181537 is a deficient number, since it is larger than the sum of its proper divisors (1).

81181537 is an equidigital number, since it uses as much as digits as its factorization.

81181537 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6720, while the sum is 34.

The square root of 81181537 is about 9010.0797443752. The cubic root of 81181537 is about 432.9978665310.

It can be divided in two parts, 81181 and 537, that added together give a palindrome (81718).

The spelling of 81181537 in words is "eighty-one million, one hundred eighty-one thousand, five hundred thirty-seven".