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A145607
Numbers k such that (3*(2*k + 1)^2 + 2)/5 is a square.
2
0, 4, 35, 279, 2200, 17324, 136395, 1073839, 8454320, 66560724, 524031475, 4125691079, 32481497160, 255726286204, 2013328792475, 15850904053599, 124793903636320, 982500325036964, 7735208696659395, 60899169248238199
OFFSET
1,2
COMMENTS
Square roots of (3*(2*k+1)^2+2)/5 are listed in A070997, therefore (3*(2*a(n) + 1)^2 + 2)/5 = A070997(n-1)^2.
FORMULA
a(n+2) = 8*a(n+1) - a(n) + 3.
From R. J. Mathar, Oct 24 2008: (Start)
G.f.: x^2*(4 - x)/((1 - x)*(1 - 8*x + x^2)).
a(n) = (A057080(n-1)-1)/2. (End)
CROSSREFS
Cf. A001091 (first differences).
Sequence in context: A261186 A104526 A174436 * A188527 A292190 A026304
KEYWORD
nonn,easy
AUTHOR
Richard Choulet, Oct 14 2008
EXTENSIONS
a(4) corrected, extended, definition corrected by R. J. Mathar, Oct 24 2008
Offset changed by Bruno Berselli, Apr 06 2018
STATUS
approved