81491237 has 2 divisors, whose sum is σ = 81491238. Its totient is φ = 81491236.

The previous prime is 81491203. The next prime is 81491239. The reversal of 81491237 is 73219418.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 41977441 + 39513796 = 6479^2 + 6286^2 .

It is a cyclic number.

It is not a de Polignac number, because 81491237 - 2¹² = 81487141 is a prime.

Together with 81491239, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 81491197 and 81491206.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81491239) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40745618 + 40745619.

It is an arithmetic number, because the mean of its divisors is an integer number (40745619).

Almost surely, 2^81491237 is an apocalyptic number.

It is an amenable number.

81491237 is a deficient number, since it is larger than the sum of its proper divisors (1).

81491237 is an equidigital number, since it uses as much as digits as its factorization.

81491237 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 12096, while the sum is 35.

The square root of 81491237 is about 9027.2496919051. The cubic root of 81491237 is about 433.5477833351.

The spelling of 81491237 in words is "eighty-one million, four hundred ninety-one thousand, two hundred thirty-seven".