#include <cmath>#include <iomanip>#include <iostream>#include <limits>#include <numbers>#include <string_view> auto egamma_aprox(constunsigned iterations){longdouble s{};for(unsigned m{2}; m!= iterations;++m)if(constlongdouble t{std::riemann_zetal(m)/ m}; m%2)            s-= t;else            s+= t;return s;}; int main(){usingnamespace std::numbers;usingnamespace std::string_view_literals; constauto x=std::sqrt(inv_pi)/ inv_sqrtpi+std::ceil(std::exp2(log2e))+ sqrt3* inv_sqrt3+std::exp(0);constauto v=(phi* phi- phi)+1/std::log2(sqrt2)+        log10e* ln10+std::pow(e, ln2)-std::cos(pi);std::cout<<"The answer is "<< x* v<<'\n'; constexprauto γ{"0.577215664901532860606512090082402"sv};std::cout<<"γ as 10⁶ sums of ±ζ(m)/m   = "<< egamma_aprox(1'000'000)<<'\n'<<"γ as egamma_v<float>       = "<<std::setprecision(std::numeric_limits<float>::digits10+1)<< egamma_v<float><<'\n'<<"γ as egamma_v<double>      = "<<std::setprecision(std::numeric_limits<double>::digits10+1)<< egamma_v<double><<'\n'<<"γ as egamma_v<long double> = "<<std::setprecision(std::numeric_limits<longdouble>::digits10+1)<< egamma_v<longdouble><<'\n'<<"γ with "<< γ.length()-1<<" digits precision = "<< γ<<'\n';}

The answer is 42γ as 10⁶ sums of ±ζ(m)/m   = 0.577215γ as egamma_v<float>       = 0.5772157γ as egamma_v<double>      = 0.5772156649015329γ as egamma_v<long double> = 0.5772156649015328606γ with 34 digits precision = 0.577215664901532860606512090082402