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A262025 a(n) = (A262024(n)-1)/2: a(n)*(a(n) + 1) = d(n)*Y(n)^2 with d(n) = A007969 and Y(n) =  A261250(n). 3
1, 4, 2, 9, 3, 324, 7, 16, 8, 4, 27, 98, 25, 63, 4900, 5, 11, 17, 36, 18, 12, 1024, 6, 99, 80, 12167, 49, 324, 33124, 242, 44, 7, 75, 9801, 15, 883159524, 31, 64, 32, 16, 3887, 125, 8, 1140624, 1849, 28899, 175, 26, 81, 27, 142884, 5202, 250000, 9, 575, 6075, 1071647, 19, 31404816, 49, 100, 50, 20, 16040025, 675, 79035335993124, 10, 147, 63, 602176, 512, 4900, 324, 153458 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The positive fundamental solutions (x0(n), y0(n)) of the Pell equation x^2 - d(n) y^2 = +1, with d not a square, have only even y solutions for d(n) = A007969 (Conway's products of 1-happy couples). The proof is now given in the W. Lang link under A007969. The solutions x0 and  y0 = 2*Y0 are given in A262024 and 2*A261250, respectively. The numbers X0(n) = (x0(n) -  1)/2 = a(n) satisfy a(n)*(a(n) + 1) = d(n)*Y0(n)^2. See the mentioned link.

LINKS

Table of n, a(n) for n=1..74.

CROSSREFS

Cf. A007969, A007970, A262024, A261250.

Sequence in context: A076022 A064421 A051494 * A118013 A157647 A194108

Adjacent sequences:  A262022 A262023 A262024 * A262026 A262027 A262028

KEYWORD

nonn

AUTHOR

Wolfdieter Lang, Sep 19 2015

STATUS

approved

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Last modified August 15 12:26 EDT 2020. Contains 336496 sequences. (Running on oeis4.)