[foxes]

  let y=3n*(10n**1000020n);
  const f=(i,x,p)=>{(x>0)?f(i+2n,x*i/((i+1n)*4n),p+x/(i+2n)):p/(10n**20n)} 
  console.log(f(1n,y/8n,y));

Not sure if I can golf it anymore

[minitech]

That version already doesn’t work… once you fix the arrow function, there’s also the issue that most engines today don’t support proper tail calls, so nothing recursive will be portable. (But if it did, you could save a lot of characters by dropping unnecessary parentheses, expanding (i+1n)×4n to 4n×i+4n, replacing the const with a comma, removing semicolons…)

[sqnguyen]

this is my perl golf version of the same series. You can probably can do something similar with js:

map$l+=(-1)$_/(1-$_2)4,1..<>;die$l

[NieDzejkob]

Doesn't work for me [0]. Perhaps HN messed it up somehow?

[0]: https://tio.run/##K0gtyjH9/z83sUAlR9tWQ9dQUyVeX8NQVyXeSNNEx1...

[sqnguyen]

I guess so... https://tio.run/##K0gtyjH9/z83sUAlR9tWQ9dQU0tLJV5fw1BXJV7LSF...

[mkl]

To post code, indent it with two spaces, or HN will turn asterisks into italics on/off.