81591533 has 2 divisors, whose sum is σ = 81591534. Its totient is φ = 81591532.

The previous prime is 81591527. The next prime is 81591541. The reversal of 81591533 is 33519518.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 47637604 + 33953929 = 6902^2 + 5827^2 .

It is a cyclic number.

It is not a de Polignac number, because 81591533 - 2⁶ = 81591469 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 81591493 and 81591502.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81591563) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40795766 + 40795767.

It is an arithmetic number, because the mean of its divisors is an integer number (40795767).

Almost surely, 2^81591533 is an apocalyptic number.

It is an amenable number.

81591533 is a deficient number, since it is larger than the sum of its proper divisors (1).

81591533 is an equidigital number, since it uses as much as digits as its factorization.

81591533 is an evil number, because the sum of its binary digits is even.

The product of its digits is 16200, while the sum is 35.

The square root of 81591533 is about 9032.8031640239. The cubic root of 81591533 is about 433.7255745644.

The spelling of 81591533 in words is "eighty-one million, five hundred ninety-one thousand, five hundred thirty-three".