"Doubly triangular number"@en . . . . . "66308569"^^ . . . . . . . . . . . "1122559291"^^ . . . . . . . . . . . "In mathematics, the doubly triangular numbers are the numbers that appear within the sequence of triangular numbers, in positions that are also triangular numbers. That is, if denotes the th triangular number, then the doubly triangular numbers are the numbers of the form ."@en . . "4430"^^ . . . . "In mathematics, the doubly triangular numbers are the numbers that appear within the sequence of triangular numbers, in positions that are also triangular numbers. That is, if denotes the th triangular number, then the doubly triangular numbers are the numbers of the form ."@en . .