Proof without words:
Nelsen, Roger B.
Proof without words: each but two triangular numbers is a sum of three triangular numbers/ Roger B. Nelsen. - Washington D. C.: Mathematical Association of America, cJul 2012-Sept 2015. - v43 n3, page 172: Illustrations; 25 cm.
0746-8342
Mathematics--Triangular number.
DPer 510.5 C697 Jan 2012-Sept 2015 v. 43 & 46, n. 1-4
Proof without words: each but two triangular numbers is a sum of three triangular numbers/ Roger B. Nelsen. - Washington D. C.: Mathematical Association of America, cJul 2012-Sept 2015. - v43 n3, page 172: Illustrations; 25 cm.
0746-8342
Mathematics--Triangular number.
DPer 510.5 C697 Jan 2012-Sept 2015 v. 43 & 46, n. 1-4