81971557 has 2 divisors, whose sum is σ = 81971558. Its totient is φ = 81971556.

The previous prime is 81971537. The next prime is 81971573. The reversal of 81971557 is 75517918.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 80892036 + 1079521 = 8994^2 + 1039^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81971557 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81971507) 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, 40985778 + 40985779.

It is an arithmetic number, because the mean of its divisors is an integer number (40985779).

Almost surely, 2^81971557 is an apocalyptic number.

It is an amenable number.

81971557 is a deficient number, since it is larger than the sum of its proper divisors (1).

81971557 is an equidigital number, since it uses as much as digits as its factorization.

81971557 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 88200, while the sum is 43.

The square root of 81971557 is about 9053.8144999773. The cubic root of 81971557 is about 434.3979110252.

It can be divided in two parts, 81971 and 557, that added together give a palindrome (82528).

The spelling of 81971557 in words is "eighty-one million, nine hundred seventy-one thousand, five hundred fifty-seven".