81501691 has 2 divisors, whose sum is σ = 81501692. Its totient is φ = 81501690.

The previous prime is 81501671. The next prime is 81501701. The reversal of 81501691 is 19610518.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81501691 - 2¹¹ = 81499643 is a prime.

It is not a weakly prime, because it can be changed into another prime (81501671) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40750845 + 40750846.

It is an arithmetic number, because the mean of its divisors is an integer number (40750846).

Almost surely, 2^81501691 is an apocalyptic number.

81501691 is a deficient number, since it is larger than the sum of its proper divisors (1).

81501691 is an equidigital number, since it uses as much as digits as its factorization.

81501691 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2160, while the sum is 31.

The square root of 81501691 is about 9027.8286979761. The cubic root of 81501691 is about 433.5663215849.

The spelling of 81501691 in words is "eighty-one million, five hundred one thousand, six hundred ninety-one".