Saturday, 22 March 2014

mathematics - Make numbers 1 - 32 using the digits 2, 0, 1, 7


This is similar to the "Four fours" puzzle, but using the digits 2, 0, 1 and 7.


Rules:



  • Use all four digits exactly once

  • Allowed operations: +, -, x, ÷, ! (factorial), exponentiation, square root

  • Parentheses and grouping (e.g. "21") are also allowed

  • Squaring uses the digit 2 so expressions using multiple twos, like 22 or 12+72, are not allowed


  • Keep the order "2017" in at least 16 expressions (and more if you can!)


Good luck and Happy New Year!




Similar question for 2016



Answer



This answer has 29 expressions with the "2017" order. Those NOT in order are denoted by sadness - :(



1=20+17

2=20+17

3=2+0+17

4=2+01+7

5=2+(01)+7

6=(20)1+7

7=201+7

8=(20)+1+7

9=2+(01)+7

10=2+0+1+7

11=2+0!+1+7

12=(2+0)(1+7)

13=(2+0+1)!+7

14=(2+0!)!+1+7

15=2+0+17 (Improved for order by Ivo Beckers)

16=((20)!)+17

17=(20)+17

18=(20)+17

19=2+0+17

20=2+0!+17

21=20+17

22=2+((0!17))! (Improved by Pratheek B!)

23=(2+0!)!+17

24=(2+0!)(1+7)

25=(710!)2 :(

26=201+7

27=20+(17)

28=20+1+7

29=27+(1+0!) :(

30=102+7 :(

31=(2+0!+1)!+7

32=2(0!)1+7




FOOLING AROUND (I'm simply curious about how far we can go)



33=1720!

34=(2+0)17 :D

35=((2+0!)!1)7 (Improved by Christoph!)

36=(71+0)2

37=20+17 :D

38=???

39=7210



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