81801649 has 2 divisors, whose sum is σ = 81801650. Its totient is φ = 81801648.

The previous prime is 81801623. The next prime is 81801659. The reversal of 81801649 is 94610818.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 66341025 + 15460624 = 8145^2 + 3932^2 .

It is a cyclic number.

It is not a de Polignac number, because 81801649 - 2⁷ = 81801521 is a prime.

It is not a weakly prime, because it can be changed into another prime (81801619) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40900824 + 40900825.

It is an arithmetic number, because the mean of its divisors is an integer number (40900825).

Almost surely, 2^81801649 is an apocalyptic number.

It is an amenable number.

81801649 is a deficient number, since it is larger than the sum of its proper divisors (1).

81801649 is an equidigital number, since it uses as much as digits as its factorization.

81801649 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 13824, while the sum is 37.

The square root of 81801649 is about 9044.4264052509. The cubic root of 81801649 is about 434.0975680885.

The spelling of 81801649 in words is "eighty-one million, eight hundred one thousand, six hundred forty-nine".