81811651 has 2 divisors, whose sum is σ = 81811652. Its totient is φ = 81811650.

The previous prime is 81811589. The next prime is 81811657. The reversal of 81811651 is 15611818.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81811651 - 2¹³ = 81803459 is a prime.

It is not a weakly prime, because it can be changed into another prime (81811657) 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, 40905825 + 40905826.

It is an arithmetic number, because the mean of its divisors is an integer number (40905826).

Almost surely, 2^81811651 is an apocalyptic number.

81811651 is a deficient number, since it is larger than the sum of its proper divisors (1).

81811651 is an equidigital number, since it uses as much as digits as its factorization.

81811651 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1920, while the sum is 31.

The square root of 81811651 is about 9044.9793255706. The cubic root of 81811651 is about 434.1152599361.

The spelling of 81811651 in words is "eighty-one million, eight hundred eleven thousand, six hundred fifty-one".