81551633 has 2 divisors, whose sum is σ = 81551634. Its totient is φ = 81551632.

The previous prime is 81551581. The next prime is 81551647. The reversal of 81551633 is 33615518.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 76247824 + 5303809 = 8732^2 + 2303^2 .

It is a cyclic number.

It is not a de Polignac number, because 81551633 - 2¹⁴ = 81535249 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81551633.

It is not a weakly prime, because it can be changed into another prime (81551033) 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, 40775816 + 40775817.

It is an arithmetic number, because the mean of its divisors is an integer number (40775817).

Almost surely, 2^81551633 is an apocalyptic number.

It is an amenable number.

81551633 is a deficient number, since it is larger than the sum of its proper divisors (1).

81551633 is an equidigital number, since it uses as much as digits as its factorization.

81551633 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 10800, while the sum is 32.

The square root of 81551633 is about 9030.5942772334. The cubic root of 81551633 is about 433.6548626841.

The spelling of 81551633 in words is "eighty-one million, five hundred fifty-one thousand, six hundred thirty-three".