A few martingale oriented inverse utility functions.

bet-utils.js

const getBaseBetFromCurrent = (wager, multi, streak) => (wager / (multi ^ streak)); 

const getBetSizeForStreak = (base, multi, streak) => (base * (multi ^ streak));

const getStreakSizeFromBet = (base, wager, multi) => (Math.log(wager / base) / Math.log(multi));

const getPrevBetFromLastBet = (wager, multi) => (wager / multi);

const getBetMultiFromPrevBet = (wager, prev) => (wager / prev);

const getBetMultiForPayout = (payout) => (payout / (payout - 1));

const getPayoutFromBetMulti = (multi) => (multi / (multi - 1));