81631217 has 2 divisors, whose sum is σ = 81631218. Its totient is φ = 81631216.

The previous prime is 81631211. The next prime is 81631219. The reversal of 81631217 is 71213618.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 71639296 + 9991921 = 8464^2 + 3161^2 .

It is a cyclic number.

It is not a de Polignac number, because 81631217 - 2⁸ = 81630961 is a prime.

Together with 81631219, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81631217.

It is not a weakly prime, because it can be changed into another prime (81631211) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40815608 + 40815609.

It is an arithmetic number, because the mean of its divisors is an integer number (40815609).

Almost surely, 2^81631217 is an apocalyptic number.

It is an amenable number.

81631217 is a deficient number, since it is larger than the sum of its proper divisors (1).

81631217 is an equidigital number, since it uses as much as digits as its factorization.

81631217 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2016, while the sum is 29.

The square root of 81631217 is about 9034.9995572772. Note that the first 3 decimals coincide. The cubic root of 81631217 is about 433.7958807809.

The spelling of 81631217 in words is "eighty-one million, six hundred thirty-one thousand, two hundred seventeen".