81815381 has 2 divisors, whose sum is σ = 81815382. Its totient is φ = 81815380.

The previous prime is 81815309. The next prime is 81815389. The reversal of 81815381 is 18351818.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 73376356 + 8439025 = 8566^2 + 2905^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81815381 is a prime.

It is a super-2 number, since 2×81815381² = 13387513136350322, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81815389) 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, 40907690 + 40907691.

It is an arithmetic number, because the mean of its divisors is an integer number (40907691).

Almost surely, 2^81815381 is an apocalyptic number.

It is an amenable number.

81815381 is a deficient number, since it is larger than the sum of its proper divisors (1).

81815381 is an equidigital number, since it uses as much as digits as its factorization.

81815381 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 7680, while the sum is 35.

The square root of 81815381 is about 9045.1855149577. The cubic root of 81815381 is about 434.1218573066.

The spelling of 81815381 in words is "eighty-one million, eight hundred fifteen thousand, three hundred eighty-one".