Sequence - stop at 90

Question

You start with 0 and then proceed as follows:

1, 8, 2, 1, 11, 9, 18, ??, 90

There's no other number after 90 in this sequence. In fact, it's impossible to find!
One of the numbers can be replaced by another number, but this sequence would take up alot more space if so, so I made an exception and made it simpler.

So, what is the rule of this sequence? What number is the exception(why)? And what two-digit number is missing?

EDIT: Made a mistake in the sequence! It's correct now. Guess, it will be easier now...

$\begingroup$ Does this need some kind of knowledge-related tag? $\endgroup$
– Stiv
Commented Mar 17, 2020 at 12:12 — Stiv, Commented Mar 17, 2020 at 12:12
$\begingroup$ No, not really. Its almost completely basic knowledge. $\endgroup$
– Prim3numbah
Commented Mar 17, 2020 at 12:44 — Prim3numbah, Commented Mar 17, 2020 at 12:44

ItsPete · Accepted Answer · 2020-03-18 14:13:52Z

7

The rule is:

All numbers begin with the letter the previous one ends with

Thanks to @Stiv, we also know that:

The number chosen is the lowest 1 or 2-digit number beginning with that letter that isn't already in the sequence.

Starting with 0:

Zero > One > Eight > Two > One > Eleven > Nine > Eighteen > Nineteen > Ninety

You can't go further because

no number begins with y

This may not be all there is to it though.

answered Mar 17, 2020 at 13:43

ItsPete

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$\begingroup$ You got the correct rule! But not the correct missing two-digit number. How about the exception? $\endgroup$
– Prim3numbah
Commented Mar 17, 2020 at 13:57
1

$\begingroup$ another could be rot13(avargrra). Nice work. :) $\endgroup$
– MacGyver88
Commented Mar 17, 2020 at 13:59
1

$\begingroup$ But still, why exactly these numbers? Alot more resoning needed! $\endgroup$
– Prim3numbah
Commented Mar 17, 2020 at 14:08
2

$\begingroup$ Like @MacGyver88 says your missing number is probably rot13(avargrra - vg'f gur YBJRFG ahzore bs srjre guna 3 qvtvgf ortvaavat jvgu gur ynfg yrggre bs gur cerivbhf, hfvat ahzoref guhf-sne-hahfrq vs ninvynoyr. 1 vf ercrngrq orpnhfr vg vf gur bayl bar ortvaavat jvgu B. V'z thrffvat gur BC yvzvgrq gur ehyr gb ahzoref bs srjre guna 3 qvtvgf, ryfr gurl'q unir unq bar-uhaqerq nsgre gur 2, juvpu jbhyq grezvangr gur frdhrapr noehcgyl, fvapr ab ybj ahzoref ortva jvgu Q.) Not sure about the exception - this rule seems pretty solid unless I've missed something amongst its constraints! $\endgroup$
– Stiv
Commented Mar 17, 2020 at 15:06
$\begingroup$ @Stiv, pretty sure you nailed it. $\endgroup$
– MacGyver88
Commented Mar 17, 2020 at 15:19

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