1,31,253,991,2731 1,222,738,1740,2742 These are the difference of the numbers in above series. So, the first one should be 30. And how did you get 2742? 516,1002 so now, 1740+991=2731 so 2731+2742=5473

No idea. I couldn't find the sequence in the OP at http://www.research.att.com/~njas/sequences but swapping the commas for spaces they all showed up in only one sequence http://www.research.att.com/~njas/s...+2731&sort=0&fmt=0&language=english&go=Search and there were 2,5,8,11 numbers between them. 2,5,8,11 shows up in 65 sequences and has varying numbers after it, but 14 seems common. So this leads to my guess of 6121.

Ans is 6121. 31-1 = 30 = (3)^3 +3 253-31 = 222 = (6)^3 + 6 991 -253 = 738 = (9)^3 + 9 2731 - 991 =1740 =(12)^3 + 12 so te ans will be 2731 + (15)^3 + 15 =6121

Thanks Mayjune and congrats xpi0t0s. By the way what was your logic while calculating 6121? The same as of mine??

Heh, no, I did it in a spreadsheet and made a BIG assumption...column A contained the original sequence in A1-A5; B2=A2-A1 and copied the formula to B3-B5, C3-C5, D4-D5 and E5. I assumed that was the end of it and that the next row, if it existed, would end with E6=E5 and worked backwards to find out what would be in D6, C6, B6 and A6, and that's where I got 6121 from. Then I looked up the sequence in the sequences database as explained (and linked) earlier in the thread.