MathDB
Sequence

Source:

February 27, 2008
functioninduction

Problem Statement

Let {ak} \{a_k\} be a sequence of integers such that a_1 \equal{} 1 and a_{m \plus{} n} \equal{} a_m \plus{} a_n \plus{} mn, for all positive integers m m and n n. Then a12 a_{12} is <spanclass=′latex−bold′>(A)</span> 45<spanclass=′latex−bold′>(B)</span> 56<spanclass=′latex−bold′>(C)</span> 67<spanclass=′latex−bold′>(D)</span> 78<spanclass=′latex−bold′>(E)</span> 89 <span class='latex-bold'>(A)</span>\ 45 \qquad <span class='latex-bold'>(B)</span>\ 56 \qquad <span class='latex-bold'>(C)</span>\ 67 \qquad <span class='latex-bold'>(D)</span>\ 78 \qquad <span class='latex-bold'>(E)</span>\ 89
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