数学常数

#include <cmath>
#include <iomanip>
#include <iostream>
#include <limits>
#include <numbers>
#include <string_view>
 
auto egamma_aprox(const unsigned iterations)
{
    long double s = 0;
    for (unsigned m = 2; m < iterations; ++m)
    {
        if (const long double t = std::riemann_zetal(m) / m; m % 2)
            s -= t;
        else
            s += t;
    }
    return s;
};
 
int main()
{
    using namespace std::numbers;
 
    const auto x = std::sqrt(inv_pi) / inv_sqrtpi +
        std::ceil(std::exp2(log2e)) + sqrt3 * inv_sqrt3 + std::exp(0);
    const auto v = (phi * phi - phi) + 1 / std::log2(sqrt2) +
        log10e * ln10 + std::pow(e, ln2) - std::cos(pi);
 
    std::cout << "答案是 " << x * v << '\n';
 
    using namespace std::string_view_literals;
    constexpr auto γ = "0.577215664901532860606512090082402"sv;
 
    std::cout
        << "γ 按 10⁶ 个 ±ζ(m)/m 的和    = "
        << egamma_aprox(1'000'000) << '\n'
        << "γ 按 egamma_v<float>       = "
        << std::setprecision(std::numeric_limits<float>::digits10 + 1)
        << egamma_v<float> << '\n'
        << "γ 按 egamma_v<double>      = "
        << std::setprecision(std::numeric_limits<double>::digits10 + 1)
        << egamma_v<double> << '\n'
        << "γ 按 egamma_v<long double> = "
        << std::setprecision(std::numeric_limits<long double>::digits10 + 1)
        << egamma_v<long double> << '\n'
        << "γ 具 " << γ.length() - 1 << " 位精确数字          = " << γ << '\n';
}