MathDB

4

Part of 1988 ITAMO

Problems(1)

terms of 1,11,111,1111,... base 9 are triangular

Source: ITAMO 1988 p4

2/2/2020
Show that all terms of the sequence 1,11,111,1111,...1,11,111,1111,... in base 99 are triangular numbers, i.e. of the form m(m+1)2\frac{m(m+1)}{2} for an integer mm
Triangular numbernumber theory