Sequence Generator

Fixed step and fixed ratio

A fixed step adds the same amount each time. Start 100, step 50, count 5 gives 100, 150, 200, 250, 300. Negative steps count down and decimals work. Fill in the stop value and the count is worked out from the range instead: the sequence runs until adding another step would pass the stop, so if the stop is not exactly on a step the list ends just before it. Where that produces more than a thousand items the list is cut and the result says by how much.

A fixed ratio multiplies instead. Start 1,000 with a ratio of 1.05 gives a five percent compounding series, which is the quick way to eyeball a rate rise or an interest schedule. Values are rounded to ten decimal places, and a ratio much above one runs out of digits quickly; when a value exceeds what a double can hold the list stops early and tells you.

Dates and the end-of-month problem

Weeks are just seven-day steps, so the weekday stays fixed and a "every second Tuesday" list falls out of an interval of 2 with the unit set to weeks. Months are harder, because adding a month to 31 January has no correct answer. This tool always counts months from the original start date rather than from the previous result. Starting on 31 January, the next value is 28 or 29 February, and the one after that is 31 March, not 28 March. Chaining month-by-month from each result instead would drag the whole sequence permanently down to the 28th, which is almost never what anyone means.

The long format includes the weekday in brackets, which is worth using when the list is going into a schedule; it makes a date landing on a weekend obvious without cross-checking a calendar.

Padded numbers, and why the width matters

Zero padding exists for sorting. Anything that sorts as text puts 100 before 99, because it compares character by character and 1 comes before 9. Padding to a fixed width makes the text order match the numeric order, so 001 through 100 stay in sequence in a filename list, a spreadsheet column formatted as text, or a folder view. Pick a width with room to grow: if you might reach four digits, use four now, because renumbering later is worse than a leading zero you did not need. The tool warns when the last number in your list would overflow the width you chose.

Prefix and suffix wrap every item, which is what turns a padded list into INV-001 or 2026-001-A. They are applied after the number is built, so they never interfere with the padding.

The random mode is a different kind of thing

Every other mode here is deterministic: the same inputs give the same list forever. Random mode is not, and it uses the same machinery as the random number generator on this site: crypto.getRandomValues() where the browser has it, reduced into your range by rejection sampling so no value is favoured, with a Fisher-Yates shuffle behind the no-repeats option. The Source line in the result says which generator actually ran.

That still does not make it a draw anyone else can trust. A list of numbers on your screen carries no evidence of how it was produced, and rebuilding until a pleasing set appears leaves no trace. For a raffle, an allocation, or anything where somebody loses out, draw physically in front of the people involved or publish a seed before the draw so the result can be recomputed independently afterwards.

Building more than a thousand

The cap is a thousand items per build, chosen so the page renders and copies without stalling. Longer runs are a matter of doing it twice: build 1 to 1,000, then change the start to 1,001 and build again, and paste the two blocks together. For the fixed-step mode with a stop value set, the first thousand are built and the result tells you how many were left over so you know where to restart. Nothing is stored between builds, so the tool has no idea which serial numbers you have already issued, and checking that against your own records stays your job.

Questions people ask