Summability factor theorems for triangular matrices
We obtain necessary and sufficient conditions for the series Sigma a(n) summable \A\ to imply that Sigma a(n)lambda(n) is summable \B\(k), and for the series Sigma(an) summable \A\(k) to imply that Sigma a(n)lambda(n) is summable \B\, k >= 1 where A and B are lower triangular matrices.
summability factor absolute summability