81997381 has 2 divisors, whose sum is σ = 81997382. Its totient is φ = 81997380.

The previous prime is 81997367. The next prime is 81997427. The reversal of 81997381 is 18379918.

It is an a-pointer prime, because the next prime (81997427) can be obtained adding 81997381 to its sum of digits (46).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 81993025 + 4356 = 9055^2 + 66^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81997381 is a prime.

It is a super-2 number, since 2×81997381² = 13447140981718322, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81997081) 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, 40998690 + 40998691.

It is an arithmetic number, because the mean of its divisors is an integer number (40998691).

Almost surely, 2^81997381 is an apocalyptic number.

It is an amenable number.

81997381 is a deficient number, since it is larger than the sum of its proper divisors (1).

81997381 is an equidigital number, since it uses as much as digits as its factorization.

81997381 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 108864, while the sum is 46.

The square root of 81997381 is about 9055.2405268993. The cubic root of 81997381 is about 434.4435232443.

The spelling of 81997381 in words is "eighty-one million, nine hundred ninety-seven thousand, three hundred eighty-one".