An octagonal number is a number that is represented by the set of figures given below.
A certain octagonal number is the sum of the squares of three terms in an arithmetic sequence with a common difference of 704. What is that octagonal number?
(In reply to For starters
This UBASIC program uses e.g.'s expressions for the square sum and the octagonal numbers:
10 for N=1 to 1000000
30 if V@3=0 and V>0 then
50 :if M*M=V/3 then
60 :print M,3*m*m+2*704*704
The result indicates the octagonal number is 25,119,920 and the middle term in the arithmetic sequence is 2,836.
25,119,920 is the 2,894-th octagonal number, based on the formula e.g. found.
Posted by Charlie
on 2006-06-13 11:07:39