What is the next number in the following series?

1, 2, 4, 13, 31, 112, ?

It appears that it's not geometric, and nothing is multiplied to get each subsequent term, unless it's multiplied then added or subtracted:
1×1+1=2
2×1+2=4 or 2×2+0=4
4×2+5=13 or 4×3+1=13
13×2+5=31
.. okay, no pattern that I can see ..

Looking at the differences:
1+1=2, 2+2=4, 4+9=13, 13+18=31, 31+73=112...
Still no help. For a second it looked like each term just added a perfect square, but that's not it.
The other thought I had was that it's the ascending sequence of numbers whose digits add up to 4 (4, 13, 22, 31, 40, 103, 112, 121, 130, 211..) but then I realized that it was missing some terms, besides the fact that the first two terms don't even fit.

Posted by DJ on 2003-08-03 07:15:58