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A307173
Second class of all proper positive solutions y2(n) = a(n) of the Pell equation x^2 - 7*y^2 = 9.
3
1, 20, 319, 5084, 81025, 1291316, 20580031, 327989180, 5227246849, 83307960404, 1327700119615, 21159893953436, 337230603135361, 5374529756212340, 85655245496262079, 1365109398183980924, 21756095125447432705, 346732412608974942356, 5525962506618151644991
OFFSET
1,2
COMMENTS
The corresponding x2 solutions are given in A307172.
See A307172 for details.
FORMULA
G.f.: x*(1 + 4*x)/(1 - 16*x + x^2).
a(n) = -4*S(n, 16) + 65*S(n-1, 16) for n >= 1, with S(n,16) = A077412(n).
a(n) = sqrt((A307172(n)^2 - 9)/7) for n >= 1.
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wolfdieter Lang, Mar 28 2019
STATUS
approved