81971537 has 2 divisors, whose sum is σ = 81971538. Its totient is φ = 81971536.

The previous prime is 81971521. The next prime is 81971557. The reversal of 81971537 is 73517918.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 58507201 + 23464336 = 7649^2 + 4844^2 .

It is a cyclic number.

It is not a de Polignac number, because 81971537 - 2⁴ = 81971521 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 81971494 and 81971503.

It is not a weakly prime, because it can be changed into another prime (81971507) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40985768 + 40985769.

It is an arithmetic number, because the mean of its divisors is an integer number (40985769).

Almost surely, 2^81971537 is an apocalyptic number.

It is an amenable number.

81971537 is a deficient number, since it is larger than the sum of its proper divisors (1).

81971537 is an equidigital number, since it uses as much as digits as its factorization.

81971537 is an evil number, because the sum of its binary digits is even.

The product of its digits is 52920, while the sum is 41.

The square root of 81971537 is about 9053.8133954704. The cubic root of 81971537 is about 434.3978756960.

The spelling of 81971537 in words is "eighty-one million, nine hundred seventy-one thousand, five hundred thirty-seven".