A363637 Indices of numbers of the form k^2-1, k >= 2, that can be written as a product of smaller numbers of that same form.

5, 11, 19, 26, 29, 31, 41, 55, 65, 71, 89, 99, 109, 127, 131, 134, 151, 155, 161, 181, 191, 209, 239, 244, 251, 265, 271, 274, 287, 289, 305, 323, 341, 349, 351, 379, 419, 449, 461, 485, 491, 505, 511, 551, 575, 599, 647, 649, 701, 703, 755, 769, 811, 846, 869

Offset: 1

Author

Pontus von Brömssen, Jun 19 2023

Keywords

• nonn

Examples

			5 is a term because 5^2-1 = 24 = 3*8 = (2^2-1)*(3^2-1)
26 is a term because 26^2-1 = 675 = 3*15*15 = (2^2-1)*(4^2-1)^2. (This is the first term that requires more than two factors.)
		

Crossrefs

Cf. A005563, A363636.