4 ms·

Freshman year of uni I memorized some variant of this, and after some practice I got to where I could do the math in 3-5 seconds. Protip: Some parts of the alg

Freshman year of uni I memorized some variant of this, and after some practice I got to where I could do the math in 3-5 seconds. Protip: Some parts of the algorithm can be subject to a CPU/Memory trade off. In the variant presented in the wiki article, steps 1 and 2 can be combined. Memorize the doomsdays for all of the years of people you're likely to want to calculate their date of birth. For me, this meant memorizing the doomsdays between say, 1980 and 1995. You can also memorize a modulo 7 table for all numbers you're likely to encounter. You can get fast enough in the amount of time it takes you to say some canned response "Hmm, I think the date X YYth of ZZZZ would fall on..." you can figure out the answer. ----- Though it turns out this is a significantly less impressive party trick as I initially imagined it'd be.

iamwil 12y ago
People aren't impressed by it?
- gamegoblin 12y ago
  Only a certain kind of people really appreciate it. Generally, the same kind of people who are impressed by rubik's cube speedsolving (which I also thought would be amazingly cool) are impressed by this. But for a lot of people, they just assume there is some simple trick to it, say "cool" and move on. And then other people assume you must be some sort of autistic savant.
  - dools 12y ago
    I found the same for the ability to divide numbers by 17 in my head... it really didn't get me a lot of action.
- eps 12y ago
  It's hard to know if the answer you are given is in fact correct unless you knew it beforehand.
  - gamegoblin 12y ago
    Fortunately, I've found that most people know which day of the week they were born on. Once or twice, though, someone was mistaken and upon consulting wolfram alpha, we determined the doomsday algorithm was correct.
- allegory 12y ago
  Most people are impressed by what a person owns or looks like, not what they are capable of or what value they can add to the world. It saddens me. I'd sit with someone who did this and learn how it works! My party trick clears the room: eye socket farts.
Borg33414625035 12y ago
Here's my formula for D/M/Y where Y=YYYY=CCFS (CC=century digits F=First S=Second digit of the last two digits in year) Note:Only for Gregorian calendar. Formula= {D +Table(M) -1 IF month=1or2&leap_year +Table(CCmod4) +Table(F) +Table(S +2 IF F is odd) } mod7 Tables are: Month {033614625035} or Jan=0 Feb=3 Mar=3 Apr=6 etc. Century {6420} or 16xx=6 17xx=4 18xx=2 19xx=0 20xx=6 etc. TableFirst memorize {0340145025} or {00,13,24,30,41,54,65,71,82,95} TableSecond memorize {012356013456} or {00,11,22,33,45,56,60,71,83,94,105,116} FormulaResultTable:1=Monday...6=Saturday 0=Sunday Example: 16 August 2014 = (16+2+6+3+0)mod7=6=Saturday In this method,I find slight advantage over "odd+11 method" because my method does not involve two digit arithmetric (and memorizing running total if you're not calculating FS first),although learning tables take some time.

iamwil 12y ago

People aren't impressed by it?

gamegoblin 12y ago
Only a certain kind of people really appreciate it. Generally, the same kind of people who are impressed by rubik's cube speedsolving (which I also thought would be amazingly cool) are impressed by this. But for a lot of people, they just assume there is some simple trick to it, say "cool" and move on. And then other people assume you must be some sort of autistic savant.
- dools 12y ago
  I found the same for the ability to divide numbers by 17 in my head... it really didn't get me a lot of action.
eps 12y ago
It's hard to know if the answer you are given is in fact correct unless you knew it beforehand.
- gamegoblin 12y ago
  Fortunately, I've found that most people know which day of the week they were born on. Once or twice, though, someone was mistaken and upon consulting wolfram alpha, we determined the doomsday algorithm was correct.
allegory 12y ago
Most people are impressed by what a person owns or looks like, not what they are capable of or what value they can add to the world. It saddens me. I'd sit with someone who did this and learn how it works! My party trick clears the room: eye socket farts.

Borg33414625035 12y ago

Here's my formula for D/M/Y where Y=YYYY=CCFS (CC=century digits F=First S=Second digit of the last two digits in year) Note:Only for Gregorian calendar. Formula= {D +Table(M) -1 IF month=1or2&leap_year +Table(CCmod4) +Table(F) +Table(S +2 IF F is odd) } mod7 Tables are: Month {033614625035} or Jan=0 Feb=3 Mar=3 Apr=6 etc. Century {6420} or 16xx=6 17xx=4 18xx=2 19xx=0 20xx=6 etc. TableFirst memorize {0340145025} or {00,13,24,30,41,54,65,71,82,95} TableSecond memorize {012356013456} or {00,11,22,33,45,56,60,71,83,94,105,116} FormulaResultTable:1=Monday...6=Saturday 0=Sunday Example: 16 August 2014 = (16+2+6+3+0)mod7=6=Saturday In this method,I find slight advantage over "odd+11 method" because my method does not involve two digit arithmetric (and memorizing running total if you're not calculating FS first),although learning tables take some time.