On-Line Encyclopedia of Integer Sequences (OEIS)

The On-Line Encyclopedia of Integer Sequences (OEIS) is a great resource for finding details on your favorite integer sequences.   Each entry contains historical information about the sequence, mathematical motivations, key people in finding or defining the sequence, literature links, and more.

A few of my favorites:

• A008578 Prime Numbers
• A000796 Decimal Expansion of Pi
• A000045 Fibonacci numbers

Another sequence that's really esoteric, but one that I have played around on with the kids:

• A250001 Number of arrangements of n circles in the affine plane.

I'll probably make a separate post about this one later.