# Equation for input

I need an equation for these set of inputs and outputs. Y will equal anything below 0 or above 9 so modulo might be needed. Also if x<0 y=0 . It's probably going to be a little complex so any common mathematical symbol can be used if needed.

>| X | Y |
>| 0 | 0 |
>| 1 | 0 |
>| 2 | 0 |
>| 3 | 0 |
>| 4 | 1 |
>| 5 | 3 |
>| 6 | 6 |
>| 7 | 2 |
>| 8 | 5 |
>| 9 | 1 |
>| 10| 2 |
>| 11| 4 |
>| 12| 9 |
>| 13| 9 |
>| 14| 8 |
>| 15| 6 |

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What do you mean "equation"? Do you mean "polynomial equation"? –  rschwieb Oct 16 '12 at 13:18

OEIS finds: $$y = \left\lfloor \frac{2^x \bmod 100}{10} \right\rfloor$$

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or rather more obviously "Next-to-least significant digit of 2^n" –  Henry Oct 11 '12 at 22:38
Well thank you i was working on a program for counting the number of digits in a number if a user inputs 2^x. But since i would need to work with more than 2 bits could you explain to me how the function changes as you look for the 3rd to least significant bit,4th to least significant bit and so on? –  Dyrand Oct 12 '12 at 2:35
Dyrand, 3rd least significant bit would be $[(2^x\bmod1000)/100]$, 4th would be $[2^x\bmod10000)/1000]$, and so on. –  Gerry Myerson Oct 12 '12 at 5:12
@Dyrand: Um, so you knew which sequence it was that you had your hand on, but held back that information so we'd have to guess and grope instead? I apologize for knowing how to use OEIS, then. –  Henning Makholm Oct 12 '12 at 11:12
Well thank you Gerry and Henning and sorry for not giving that information Henning. Also never heard of OEIS but it sure is helpful after checking it out. –  Dyrand Oct 12 '12 at 19:10