# [Haskell], <s>51</s> 49 bytes

<!-- language-all: lang-hs -->

    b#s=findIndex((<1).(`mod`256))$scanl(*)1[b,b+s..]

[Try it online!][TIO-ki98ch57]

[Haskell]: https://www.haskell.org/
[TIO-ki98ch57]: https://tio.run/##LYpBC4IwGED/ygd6@FZrNEsjyE5dAm8dTXA2xZGb4r6of28Znt578Frln3XXTcYO/UhwUaREZjxNVeDTxjh9dbr@IJ4kE1jaXpdRnDAW@odyHa6YzCterb0QxWSVcenwohuNmQt9279DqwbAO8HmDNh4AmIQAHqnf8YgR8lBMg4YcdjP3HGIl05mHpbeL5/ccjj@hziZrZi@ "Haskell – Try It Online"

Port of my [Scala answer](https://codegolf.stackexchange.com/a/210146/95792)