81871819 has 2 divisors, whose sum is σ = 81871820. Its totient is φ = 81871818.

The previous prime is 81871739. The next prime is 81871831. The reversal of 81871819 is 91817818.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81871819 - 2¹³ = 81863627 is a prime.

It is a super-2 number, since 2×81871819² = 13405989492737522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (81871859) 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, 40935909 + 40935910.

It is an arithmetic number, because the mean of its divisors is an integer number (40935910).

Almost surely, 2^81871819 is an apocalyptic number.

81871819 is a deficient number, since it is larger than the sum of its proper divisors (1).

81871819 is an equidigital number, since it uses as much as digits as its factorization.

81871819 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 32256, while the sum is 43.

The square root of 81871819 is about 9048.3047583511. The cubic root of 81871819 is about 434.2216565435.

It can be divided in two parts, 8187 and 1819, that multiplied together give a triangular number (14892153 = T₅₄₅₇).

The spelling of 81871819 in words is "eighty-one million, eight hundred seventy-one thousand, eight hundred nineteen".