Miskolc Mathematical Notes, cilt.11, sa.2, ss.183-190, 2010 (SCI-Expanded)
We obtain necessary conditions for the series ΣΣcmn, which is absolutely summable of order k by a doubly triangular matrix method A, to be such that ΣΣcmnλmn is absolutely summable of order k by a doubly triangular matrix B. © 2010 Miskolc University Press.