Feng Qi, Qing Zou, Bai-Ni Guo, THE INVERSE OF A TRIANGULAR MATRIX AND SEVERAL IDENTITIES OF THE CATALAN NUMBERS, Applicable Analysis and Discrete Mathematics, Vol. 13, No. 2 (October 2019), pp.

Drazin Inverse: A generalisation of the classical inverse applicable to singular elements, characterised by its stability under perturbations and its unique algebraic properties in Banach algebras.

Learn about how triangle sequences, quadratic sequences and the common difference with this BBC Bitesize Maths article. For students between the ages of 11 and 14.

H. P. Dikshit, Summability of a Sequence of Fourier Coefficients by a Triangular Matrix Transformation, Proceedings of the American Mathematical Society, Vol. 21, No. 1 (Apr., 1969), pp. 10-20 ...