Try to solve this on papper and you will see the pattern of numbers.

It is not the 7-th level kata. It requires knowledges of trees, which makes it the 5-th or 6-th level kata.

I have found the answear. The test mode does not work correct for Python 3.8. If you have the same error as mine, just try to test your solution on Python 3.6. It works for me.

I have te following string in test mode:
'''!(VM]bKw&@MA,fpL^dbtnSDIY)or+NsD.ag)GwhiIjzqs!RO$vs%Q[p%&z[EF~o.cJ#yur^.>qIadHMgzqbeSmRe&f$dnES)H;;zy%-Ff)ii:Oh%|$YTl+_aj'ubp)mPIDS'RkS<DU$>F_WU<MY[Rv?\^u\;,#aKo@i]UZ=St}_v_d'^YYmKzMqOBB|~/<D/iSUOe*H'wj$>!,CDMpUCP[wL}dD*lE^}GZ|W)Rs[dGVNMU}-=#C=.MW/ME]@WXH,t}LY\++eC\~#|JS'kN@!>F$j:!hHp|ceJr@+=W.[-|{~R@_O-OF?+?>xRth=*bLn]ksYya!kYf@v(@xtF@Mtm-T>xRcMJI|b/l;b.ywLG[R_HDPW&&f/H:@MFkTaOg\deTAFWkc=:rXti^hcFRQ_qz#*E{=Pn,TWNX]ZDLhIybXxu:Db|Q>I'}NCbUsOI$Djt}^*qXe\m{CLo>d{GIz%:>gLK'''

My code returns (";",2), but the answear is ('i',2). Can you explain why tha answear is "i"?

Very complex description.

Just as an example. There are two test cases from the submitting mode:
assert_equals(check_coupon('0','2014','September 5, 2014','September 25, 2014'), False);
test.assert_equals(check_coupon('123','123','September 5, 2014','October 25, 2014'), True);
test.

When I start them in Sample Tests, my code returns correct answears. But, when they are used as Basic Tests, they are not correct.
How can it be solved?
Is it my mistake or the test samples mistake?

It is too simplefor the 6-th kata. It is pure 7-th kata task.

@Blind4Basics, thank you for the advise, it has worked for my solution))

It can be solved without Sieve of Eratosthenes

The test cases contain letters which are not in abc and keyword. It is not mentioned in the instructions to the kata. The keyword can contain duplicates of letters.

Can you explain please, what the perceived value is? I do not understand this from the description.

Can I use eval and chr?

What does it mean "alternate order"? I can't understand the task. Can you please explain?

I have the following erorr for Python, when my solution is being checked.

Traceback (most recent call last):
File "main.py", line 3, in
test.assert_equals(len(add_extra([1,2])), 3)
TypeError: object of type 'NoneType' has no len()