The On-Line Encyclopedia of Integer Sequences

oeis.org

46 points·franze··7 comments

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By Neil Sloane at AT&T research

http://www.research.att.com/~njas/

I also discovered it from HN[1] :)

[1]: http://news.ycombinator.com/item?id=579925

Its first editions were in paper format:

http://www.amazon.com/Encyclopedia-Integer-Sequences-N-Sloan...

and the original, from 1973,

http://www.amazon.com/Handbook-Integer-Sequences-N-Sloane/dp...

A059893 Reverse the order of all but the most significant bits in binary expansion of n. n = 1ab..yz -> 1zy..ba = a(n).

is awesome http://oeis.org/A059893, look at the scatterplot http://oeis.org/A059893/graph

This is "because" those correspond exactly to the Hammersley sequence, a well-known quasi-random sequence of points:

http://mathworld.wolfram.com/HammersleyPointSet.html

A great resource!

If you don't have time to peruse it in depth, they have a 8.5 minute video which runs through 1000 sequences. It starts out a little slow, but some of the later examples are quite bizarre.

http://www.youtube.com/watch?v=LCWglXljevY

I once was doing a project euler challenge of some sort, and I had to find the nth term of some sequence. My code for generating the sequence was taking too long (order of hours), and I didn't feel like googling. So I downloaded the sequence from oeis and output the correct term.

Problem Solved!

Interesting you should post this, I just made a submission relating to my discovery of OEIS:

http://news.ycombinator.com/item?id=2496701

Reply on news.ycombinator.com