81815431 has 2 divisors, whose sum is σ = 81815432. Its totient is φ = 81815430.

The previous prime is 81815413. The next prime is 81815443. The reversal of 81815431 is 13451818.

Together with previous prime (81815413) it forms an Ormiston pair, because they use the same digits, order apart.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81815431 - 2¹⁷ = 81684359 is a prime.

It is a super-2 number, since 2×81815431² = 13387529499431522, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 81815393 and 81815402.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81810431) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40907715 + 40907716.

It is an arithmetic number, because the mean of its divisors is an integer number (40907716).

Almost surely, 2^81815431 is an apocalyptic number.

81815431 is a deficient number, since it is larger than the sum of its proper divisors (1).

81815431 is an equidigital number, since it uses as much as digits as its factorization.

81815431 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3840, while the sum is 31.

The square root of 81815431 is about 9045.1882788585. The cubic root of 81815431 is about 434.1219457418.

The spelling of 81815431 in words is "eighty-one million, eight hundred fifteen thousand, four hundred thirty-one".