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

1,1

Links

Table of n, a(n) for n=1..55.

Example

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.

Sequence in context: A114269 A124855 A286690 * A190756 A022823 A094693

Adjacent sequences: A363634 A363635 A363636 * A363638 A363639 A363640

Keyword

nonn

Author

Pontus von Brömssen, Jun 19 2023

Status

approved