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A335715 Squarefree numbers m such that the equation x*(x+1)*(x+2) = m*y^2 has more than one solution (x,y) with x>0 and y>0. 3
6, 210, 546, 915, 1785, 7230, 13395, 16206, 17490, 20930, 76245, 104006, 228486, 508530, 563766 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

7453355, 9147666, 19073886, 61622814, 648402306, 22023958326, 748181603526 are also terms. - Jinyuan Wang, Jul 28 2020

LINKS

Table of n, a(n) for n=1..15.

Michael A. Bennett, Lucas' square pyramid problem revisited, Acta Arithmetica 105 (2002), 341-347.

Michel Marcus and Jinyuan Wang, PARI program

EXAMPLE

6 is a term since x*(x+1)*(x+2) = 6*y^2 has 3 positive integer solutions : (1,1), (2,2) and (48,140) that give (1,1) and (24,70) for s*(s+1)*(2s+1) = 6*t^2 with a (x=2s, y=2t) variable change (see A000330 where A000330(n) = n*(n+1)*(2*n+1)/6).

CROSSREFS

Cf. A000330 (square pyramidal numbers), A005117 (squarefree numbers).

Cf. A335785 (at least one solution), A336145.

Sequence in context: A136742 A334285 A068969 * A094805 A055193 A346015

Adjacent sequences:  A335712 A335713 A335714 * A335716 A335717 A335718

KEYWORD

nonn,more

AUTHOR

Michel Marcus, Jun 18 2020

EXTENSIONS

a(12) from Michel Marcus, Jun 24 2020

a(13)-a(15) from Jinyuan Wang, Jul 28 2020

STATUS

approved

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Last modified September 26 20:34 EDT 2021. Contains 347672 sequences. (Running on oeis4.)