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arXiv · 2609.28018

On some $D(u^2)$-triples and quadruples of triangular numbers

Pavao Radić
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Abstract

We classify all $D(u^2)$-triples of triangular numbers whose smallest element is $T_{4u-1}$ or $T_{4u}$. We study the regularity of $D(N)$-triples of triangular numbers. We also show that infinitely many positive integers $u$ admit an all-triangular $D(u^2)$-quadruple. For every positive integer $k$, triangular number $T_{16k^2-1}$ belongs to infinitely many $D(u^2)$-quadruples of triangular numbers with distinct positive integer parameters $u$.

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Pavao Radić. 2026-09-23. On some $D(u^2)$-triples and quadruples of triangular numbers. https://arxiv.org/abs/2609.28018

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